MARPOL & Act to Prevent Pollution from Ships — Vessel Pollution Regulation

Every large ocean-going vessel is a potential polluter: oil residue in bilge water, sewage from crew quarters, garbage, noxious chemicals, and engine exhaust all pose environmental risks in ports, coastal zones, and the open ocean. For vessel oil spill liability beyond MARPOL's prevention rules, see Oil Pollution Act. The MARPOL Convention (International Convention for the Prevention of Pollution from Ships, 1973, modified by the 1978 Protocol — together "MARPOL 73/78") is the principal international treaty governing vessel pollution, setting standards for discharges of oil, chemicals, sewage, garbage, and air emissions from ships operating globally. The United States implements MARPOL through the Act to Prevent Pollution from Ships (APPS), codified at 33 U.S.C. §§ 1901–1915, which makes MARPOL requirements legally enforceable in U.S. waters and on U.S.-flag vessels worldwide.

MARPOL enforcement in U.S. ports has produced some of the largest criminal prosecutions in maritime history — including cases where shipping companies falsified their Oil Record Books to conceal illegal overboard discharges of oily bilge water, resulting in hundreds of millions of dollars in criminal fines and company-wide probation. The "magic pipe" cases — named for the hidden bypass pipes some vessels used to discharge oil sludge directly overboard instead of using the legally required oil-water separators — became a major enforcement focus of the Coast Guard and DOJ in the 2000s and 2010s.

Current Law (2026)

MARPOL's Six Annexes

MARPOL is organized into six annexes, each addressing a different type of vessel pollution. The U.S. has ratified all six, implementing each through APPS and associated regulations.

Annex I — Oil

The foundational annex. Governs the discharge of oil and oily mixtures from vessels. Every vessel over a certain size must:

• Maintain an Oil Record Book (ORB) documenting every transfer, discharge, and disposal of oil and oily residues — inspectors can audit these records port by port
• Use an Oily Water Separator (OWS) that limits overboard discharge to 15 parts per million (ppm) of oil (only allowed outside special areas, which have zero discharge limits)
• Carry oil to an onshore reception facility for proper disposal if oily water cannot be discharged
• Have a Shipboard Oil Pollution Emergency Plan (SOPEP) describing response procedures

"Magic pipe" fraud: The core enforcement mechanism — the Oil Record Book — is only as reliable as the crew's honesty. Numerous shipping companies directed crew to falsify ORBs to conceal illegal discharges made using bypass pipes that routed oily bilge water directly overboard without passing through the OWS. When whistleblowers (often crew members or disgruntled junior officers) reported these practices to the Coast Guard, federal prosecutions followed. Cases against companies including Carnival Cruise Lines ($40 million, 2002), Norwegian Cruise Line ($1 million fine plus probation), Royal Caribbean ($18 million, 1999), and numerous tanker operators have resulted in corporate guilty pleas and deferred prosecution agreements, with conditions including compliance monitors on vessels.

Annex II — Noxious Liquid Substances (NLS)

Governs chemical tankers carrying noxious liquid substances in bulk. Chemicals are categorized by hazard (X, Y, Z, or non-regulated) with discharge standards varying by category. Chemical tankers must carry a Cargo Record Book and use tank-washing procedures approved under the annex. Discharge of Category X substances (most hazardous) is prohibited even after washing; Categories Y and Z have discharge standards based on concentration, location (distance from coast), and ship speed. The U.S. Coast Guard enforces Annex II through inspections of cargo record books and tank washing documentation.

Annex III — Harmful Substances in Packaged Form

Governs transport of harmful substances (as defined under the IMDG Code — International Maritime Dangerous Goods) in packaged form, freight containers, portable tanks, and road/rail cars. Sets requirements for marking, labeling, documentation, stowage, quantity limits, and exceptions. The U.S. implements Annex III requirements through 46 C.F.R. Parts 146-148 (transportation of dangerous goods). This annex applies to cargo shipping, not bulk liquid tankers (which are covered by Annexes I and II).

Annex IV — Sewage from Ships

Restricts the discharge of untreated sewage into the sea. Ships over certain sizes must either:

• Discharge sewage through an approved sewage treatment plant (certified to treat sewage to defined standards), or
• Discharge into a reception facility at port, or
• Use a comminuter-disinfection system (for limited distance/speed conditions only)

Sewage cannot be discharged within 3 nautical miles of the nearest land (treated sewage) or 12 nautical miles (untreated sewage). The U.S. separately regulates vessel sewage through Clean Water Act § 312 (33 U.S.C. § 1322), which governs "marine sanitation devices" on vessels — the interplay between MARPOL Annex IV and § 312 creates a layered regulatory framework.

Annex V — Garbage from Ships

Prohibits the discharge of plastics into the sea anywhere in the world — one of the most significant global plastic pollution regulations. The annex also restricts discharge of other garbage (food waste, paper, glass, metal, operational waste) based on distance from land and whether the garbage has been processed. Ships must:

• Maintain a Garbage Management Plan
• Keep a Garbage Record Book documenting all garbage discharges and disposals
• Post notices for crew about discharge requirements

The Annex V prohibition on plastic disposal at sea has been in place since 1988 — making it one of the earliest global plastic regulation frameworks — though enforcement on the open ocean remains challenging. Port reception facilities must be adequate to receive vessel garbage; inadequate reception facilities drive illegal dumping. The Coast Guard audits Garbage Record Books during Port State Control inspections.

Annex VI — Air Pollution from Ships

The newest annex (entered into force 2005; significantly strengthened in subsequent years), governing air emissions from ships:

Sulfur Oxides (SOx): Ships must use fuel with a maximum sulfur content depending on where they operate:

• Emission Control Areas (ECAs): 0.10% sulfur maximum (or equivalent — using approved exhaust gas cleaning systems "scrubbers," or alternative fuels like LNG)
• Global waters: 0.50% sulfur maximum (the "IMO 2020" rule, in force since January 1, 2020 — a dramatic tightening from the previous 3.5% global limit)

The North American ECA covers waters within 200 nautical miles of the U.S. and Canadian coastlines (with certain exclusions). Vessels transiting this zone — including cargo ships, tankers, and cruise ships — must switch to 0.10% sulfur fuel or use scrubbers or LNG propulsion. The North American ECA has significantly improved air quality in U.S. coastal communities near major shipping lanes.

Nitrogen Oxides (NOx): Engine-specific NOx limits apply to marine diesel engines based on their rated speed. Tier I, II, and III limits progressively tighten. Tier III (the most stringent) applies to engines installed after January 1, 2016, operating in designated NOx ECAs.

VOCs, Ozone Depleting Substances, and Shipboard Incineration: Annex VI also restricts volatile organic compound (VOC) emissions from tankers, prohibits shipboard incineration of certain materials, and requires phaseout of ozone-depleting substances in ship systems.

Greenhouse Gas (GHG) Reduction: IMO's 2023 Revised GHG Strategy (adopted July 7, 2023) sets a goal of net-zero GHG emissions from international shipping "by or around 2050," with indicative checkpoints of at least 20% (striving for 30%) by 2030 and at least 70% (striving for 80%) by 2040 compared to 2008 levels — a major strengthening from the 2018 Initial Strategy's 50%-by-2050 goal. The IMO Net-Zero Framework was approved at MEPC 83 (April 2025) and is on track for formal adoption in October 2025 with entry into force in 2027 for ships over 5,000 GT. The Energy Efficiency Existing Ship Index (EEXI) and Carbon Intensity Indicator (CII) — in force since 2023 — require ships to demonstrate energy efficiency improvements and meet annual carbon intensity ratings. These are the leading edge of international shipping decarbonization regulation.

U.S. Enforcement: Port State Control

The Coast Guard enforces MARPOL as a port state — meaning it inspects foreign-flag vessels calling at U.S. ports to verify compliance with MARPOL and other international conventions. This is called Port State Control (PSC). The Coast Guard's Port State Control program annually inspects thousands of foreign vessels, auditing:

• Oil Record Books (Annex I)
• Garbage Record Books (Annex V)
• Cargo Record Books (Annex II, for chemical tankers)
• Equipment certificates (IOPP Certificate — International Oil Pollution Prevention)
• Sewage management systems (Annex IV)
• Fuel sample testing (Annex VI sulfur content)

Vessels that fail PSC inspections can be detained in port until deficiencies are corrected. Repeated violations or serious deficiencies can result in banishment — the Coast Guard has authority to deny port entry to vessels with persistent compliance failures.

For U.S.-flag vessels: The Coast Guard exercises flag state control — enforcement authority over U.S.-flag vessels operating anywhere in the world. APPS makes MARPOL requirements applicable to U.S.-flag vessels in all waters.

Criminal Enforcement and Whistleblowers

APPS makes certain MARPOL violations federal crimes. The "magic pipe" and false Oil Record Book cases illustrate how seriously federal prosecutors treat MARPOL fraud:

• Carnival Corporation (2016-2019): DOJ investigation revealed Carnival's Princess Cruises ships had been illegally dumping oily bilge water using bypass systems and falsifying records since at least 2005. Carnival pleaded guilty in 2016 to a felony charge and paid $40 million in criminal penalties. In 2019, Carnival was found in violation of its probation conditions (new violations on multiple vessels), resulting in an additional $20 million in fines and five years of additional probation with court-appointed compliance monitors.

• Generic "magic pipe" pattern: An engineer or officer discovers that ship management has ordered the installation of a bypass pipe that routes oily bilge water (normally pumped to the OWS) directly overboard, and that engineers are falsifying the ORB to show proper OWS operation. The individual refuses to participate, contacts the Coast Guard upon arrival at a U.S. port, and the ship is detained while inspectors find the pipe and verify the ORB falsifications. Criminal charges follow against the company, the chief engineer, and officers who signed false records.

Whistleblower rewards: APPS provides for awards to individuals who provide information leading to civil penalties — up to 50% of the penalty collected or $500,000, whichever is less. These rewards incentivize crew members, who have direct knowledge of aboard-ship practices, to report violations to the Coast Guard.

Implementing Regulations

The Coast Guard regulations implementing MARPOL Annex I's structural design requirements live at 33 CFR Part 157 — Rules for the Protection of the Marine Environment Relating to Tank Vessels Carrying Oil in Bulk. The Part applies to U.S.-flag oil tankers and foreign tankers operating in U.S. navigable waters or the Exclusive Economic Zone. Key provisions:

• § 157.09 — Segregated ballast tanks: new tankers of 70,000 DWT or more must have segregated ballast tanks with sufficient capacity to operate in ballast without using any cargo tanks for water ballast — the foundational rule preventing oily ballast water from being discharged at sea during ballast voyages
• § 157.10 — New tankers built after 1979 of the applicable size range must have combined segregated ballast tanks plus crude oil washing systems (using cargo oil itself as a solvent to clean tanks, dramatically reducing oil residue that would otherwise go to sea with tank washing water)
• § 157.10a — Existing tankers of 40,000 DWT or more carrying crude oil must have either segregated ballast tanks, crude oil washing, or dedicated clean ballast tanks (§ 157.10a gives vessel operators a compliance menu)
• § 157.10c — Tankships of 20,000–40,000 DWT carrying oil products face similar requirements with size-adjusted applicability
• § 157.10d — Double hull requirement: the most significant structural rule, mandating double hull construction for tank vessels contracted after June 30, 1990, or delivered after December 31, 1993. The double hull is a second skin of steel inside the vessel's outer hull, creating a void space between the two layers — so that if the outer hull is punctured in a grounding or collision, the cargo tanks are not immediately breached. This requirement was the legislative response to the Exxon Valdez grounding (1989) under the Oil Pollution Act of 1990. Subpart G provides phase-out schedules and interim measures for older single-hull vessels that predated the requirement.
• § 157.11 — Pumping, piping, and discharge arrangements: each tanker must have a fixed piping system for transferring oily mixtures to slop tanks and for discharging to reception facilities — slop tanks receive tank washing water so it can be cleaned by retention and gravity separation before any authorized overboard discharge
• § 157.12 — Oil discharge monitoring and control system: tankers must have an automated monitoring system that measures oil content of any overboard discharge in parts per million, records the rate and ship position, and prevents discharge exceeding 15 ppm except in authorized circumstances
• § 157.15 — Slop tanks: tankers must have one (smaller vessels) or two (70,000 DWT or more) slop tanks with sufficient capacity to hold tank washings and dirty ballast pending retention or authorized discharge
• § 157.19 — Cargo tank size limits: tanker cargo tanks must not exceed specified size thresholds (set by complex formulas based on vessel breadth and length) to limit the oil volume released in any single tank rupture
• Subpart D (§§ 157.41–157.79) — Crude Oil Washing systems: 39 sections governing COW system design, plan approval requirements, letter of acceptance from the administering government, operations manual, COW inspections, and shore reception of sludge — COW is one of the most effective pollution reduction tools in tanker operations because it eliminates the water needed to clean tanks (and the resulting oily water to dispose of)
• Subpart E (§§ 157.81–157.96) — Dedicated Clean Ballast Tanks: for tankers that elect this alternative to segregated ballast, detailed capacity and operational requirements ensure that ballast tanks actually stay clean and produce ballast water that can be discharged without exceeding the 15 ppm limit

Part 157 is structural and design regulation — it governs how tankers are built and equipped, not whether a particular discharge was legal on a given voyage (that is governed by the operational rules in MARPOL Annex I and the Oil Record Book requirements). The double hull rule under § 157.10d completed its phase-in by 2015, when the last grandfathered single-hull tankers in the U.S. trade were required to retrofit or retire. Today, all commercially active large crude and product tankers calling at U.S. ports are double-hulled. The combination of double hulls, segregated ballast tanks, and improved discharge monitoring has substantially reduced the oil released per vessel-mile compared to the pre-Exxon Valdez tanker fleet.

The vessel sewage framework — separate from oil pollution — lives at 33 CFR Part 159 — Marine Sanitation Devices, implementing 33 U.S.C. § 1322 (Clean Water Act § 312). The rule prohibits the discharge of untreated sewage from vessels into U.S. navigable waters and territorial seas, requiring vessels to be equipped with certified marine sanitation devices (MSDs). Three MSD types are recognized, each with distinct performance standards:

• Type I MSDs — treatment devices (maceration plus disinfection) that produce discharge with fewer than 1,000 fecal coliform bacteria per 100 mL and no visible floating solids; permissible for discharge in most U.S. waters except in No Discharge Zones
• Type II MSDs — higher-treatment biological/chemical devices requiring fewer than 200 fecal coliform per 100 mL and fewer than 150 mg/L total suspended solids; authorized in most circumstances including some waters where Type I is restricted
• Type III MSDs — holding tanks with no overboard discharge capability; required in No Discharge Zones (NDZs) that states designate under CWA § 312(f) for sensitive waters (harbors, shellfish beds, marine sanctuaries); the NDZ map is maintained by EPA and covers hundreds of designated water bodies across the country

Certification process (Subpart B): before any MSD may be sold or installed on a U.S.-documented vessel, the manufacturer must have the device certified by a USCG-recognized testing facility (Subpart D). Certification is based on performance tests — not just design review. Subpart C (39 sections — the largest subpart) prescribes the complete test protocol that recognized facilities must apply:

• §§ 159.103–159.107 — Vibration test (12 hours at resonant frequency across three axes), shock test (1,000 vertical shocks at 10g, 20–25 milliseconds duration), and rolling test (100 cycles simulating ±15° roll at 3–4 second intervals, 20% of cycles at ±30°) — simulating marine operating conditions
• § 159.109 — Pressure test: sewage retention tanks must hold water at a 7-foot pressure head (or 150% of rated operating pressure, whichever is greater) for one hour without leaking
• § 159.115 — Temperature range test: device must withstand 60°C for 16 hours and -40°C for 16 hours following winterization
• § 159.117 — Chemical resistance test: materials must demonstrate resistance to sewage, disinfectants, fuel (gasoline, diesel, mineral spirits), engine oil, ethylene glycol, and household detergents
• § 159.119 — Operability test: the device must operate at ambient temperatures from 5°C to 50°C with inlet water temperatures from 2°C to 32°C — covering temperate and tropical operating conditions

Subpart E governs cruise vessel effluent standards in Alaskan waters — a separate, stricter regime for large cruise ships (over 250 passengers or berths) operating in Alaskan waters, established following public concern about cruise ship discharges in sensitive Alaskan coastal ecosystems. Cruise vessels in Alaskan waters must use advanced wastewater treatment systems (not just Type II MSDs) and are subject to additional monitoring and reporting requirements.

The MSD certification requirement applies to all U.S.-flagged vessels with installed toilet facilities and to foreign vessels in U.S. internal waters. For recreational boaters, the practical implications are direct: boaters in NDZ waters must close all MSD discharge valves (the Coast Guard may board to verify) and use shore-based pump-out stations, which are required to be available at reasonable locations within designated NDZs. EPA's NDZ database (search at epa.gov/vessels-marinas-ports) shows whether specific waterways require Type III devices.

• 33 CFR Part 158 — Reception Facilities for Oil, Noxious Liquid Substances, and Garbage (USCG — the U.S. implementation of MARPOL Annex I, II, and V requirements for shore-based reception facilities, implementing 33 U.S.C. § 1903):

  • § 158.133 — Which ports must provide facilities: any U.S. port or terminal that receives oceangoing tankers, oil transfer operations, or vessels with garbage must maintain adequate reception facilities; "adequate" means the facility can receive vessel wastes without causing the vessel undue delay; facilities must accommodate oily bilge water and ballast water (Annex I), noxious liquid substance residues (Annex II), and garbage (Annex V) — the three MARPOL annexes with direct port-side obligations
  • § 158.135 — Certificates of Adequacy: ports and terminals subject to the reception facility requirement must hold a USCG Certificate of Adequacy (COA); the COA certifies that the port's reception facilities meet the adequacy standard; without a valid COA, a port may not legally receive oceangoing vessels covered by MARPOL; USCG Captain of the Port (COTP) may inspect reception facilities and suspend or revoke a COA for inadequate performance
  • § 158.140 — Application for a COA: applicants must describe the reception facility's physical capacity (storage volume, pumping rates, processing capability), location relative to berths, accessibility for vessels, and operational procedures; the application must demonstrate the facility can accept oil water mixtures, oily bilge water, and garbage at rates and volumes consistent with typical vessel operations at that port
  • § 158.115 — Penalties: a person who violates MARPOL 73/78, the Act, or the regulations of this part is liable for a civil penalty (APPS § 1908(b) statutory base $25,000/day, inflation-adjusted; current ceiling significantly higher) per day of violation; criminal penalties apply for intentional discharges — the penalty framework mirrors the OPA oil spill enforcement structure
  • § 158.130 — COTP authority: each USCG Captain of the Port is delegated authority to inspect reception facilities, issue and revoke COAs, and take enforcement action; COTP authority is exercised at the major port districts — COTP New York, COTP Los Angeles/Long Beach, COTP Houston/Galveston, etc.

  Part 158's reception facility regime closes the onshore half of MARPOL compliance — if vessels cannot legally discharge oily wastes, garbage, and NLS residues at port, they have no choice but to carry wastes to sea or commit illegal discharges. The USCG's Certificate of Adequacy system ensures U.S. ports maintain the infrastructure MARPOL requires. Foreign-flag vessels arriving at U.S. ports may be required to demonstrate they used reception facilities at previous ports and to provide oil record books showing compliant discharge practices — a form of port state control enforcement that extends MARPOL compliance beyond U.S. flag vessels.

• 46 CFR Part 151 — Barges Carrying Bulk Liquid Hazardous Material Cargoes (117 sections — the USCG's combined design, construction, and operational safety standard for non-self-propelled vessels (barges) carrying bulk liquid hazardous chemicals; authority: 33 U.S.C. § 1903 (APPS/MARPOL) and 46 U.S.C. § 3703 (vessel design/equipment)):

  Part 151 covers every oceangoing non-self-propelled U.S. or foreign barge operating in U.S. waters that carries bulk liquid hazardous material listed in Table 151.05 (§ 151.01-1). Table 151.05 is the operative cargo list — it catalogs hundreds of specific chemical cargoes (acids, caustics, solvents, petroleum products, petrochemicals) and assigns each a set of minimum requirements from the Part's construction, equipment, and operational subparts. Chemical tanker barges carrying Category D NLS (the lowest-hazard tier under MARPOL Annex II) must comply with Part 151's Subpart 151.12 pollution control equipment requirements, making Part 151 the barge-side implementation of MARPOL Annex II for U.S. inland and coastal waterways. Key provisions:

  • Subpart 151.04 — Inspection and Certification: a barge subject to Part 151 must hold a USCG Certificate of Inspection before operating; USCG marine inspectors examine hull integrity, tank design, pollution control equipment, cargo transfer systems, and compliance with the Table 151.05 requirements for each cargo the certificate authorizes the barge to carry; certificates must be renewed and may be revoked for non-compliance
  • Subpart 151.10 — Hull Construction Requirements: barge hull construction must meet standards for the specific cargo type — tank material compatibility (certain acids require stainless steel; oxidizers require isolation from flammable-cargo tank areas), structural integrity for cargo density, and double-skin or void-space requirements for the highest-hazard cargoes; construction standards are referenced to classification society rules
  • Subpart 151.15 — Tanks: cargo tanks must be constructed of materials compatible with the specific cargo and designed to prevent overpressure; pressure relief valve settings and gauging requirements ensure that tank pressures remain within safe limits during loading, transport, and discharge
  • Subpart 151.20 — Cargo Transfer: transfer procedures must comply with the Declaration of Inspection requirements in 33 CFR Part 156; transfer equipment must be appropriate for the specific cargo — corrosion-resistant materials for acids, grounding requirements for flammable cargoes; transfer monitoring requirements prevent overflow and accidental release
  • Subpart 151.12 — Equipment for Control of Pollution from Category D NLS Cargoes: barges carrying Category D NLS cargoes (the least hazardous MARPOL Annex II tier — substances that present a minor hazard to aquatic resources and human health) must have tank washing equipment capable of discharging wash water to a shore reception facility before unloading the remaining cargo residues; this prevents Annex II cargo residues from being discharged to the waterway as part of routine barge operations; Category D NLS requirements are the minimum Annex II compliance floor for U.S. inland barges
  • Subpart 151.50 — Special Requirements (32 sections): cargo-specific requirements supplementing the general standards — specific tank materials for listed chemicals, prohibition on co-loading incompatible cargoes (§ 151.13 Cargo Segregation), temperature control for cargoes with high freezing points or high vapor pressure requirements, and additional structural or ventilation requirements for specific reactive or toxic chemicals

  Part 151 is the operational bridge between the abstract "noxious liquid substance" framework of MARPOL Annex II and the practical safety requirements for the barges that move bulk chemicals on the Mississippi River, the Gulf Intracoastal Waterway, and U.S. coastal routes. For companies that own, charter, or operate tank barges carrying chemicals, sulfuric acid, caustic soda, or petroleum products, the Table 151.05 cargo authorization is the critical compliance document — a barge's Certificate of Inspection specifies which specific cargoes it is authorized to carry, and operating with an unauthorized cargo or without a current certificate is a USCG violation subject to civil penalties and vessel detention. Recent rulemaking: 54 FR 40040 (1989) — comprehensive revision updating construction and operational requirements; 79 FR 58284 (2014) — cargo list and Table 151.05 updates.

Implementing Regulations — Armed Forces Vessel Discharges

The EPA regulations implementing the Clean Water Act § 312(n) uniform national discharge standards for vessels of the Armed Forces live at 40 CFR Part 1700 — Uniform National Discharge Standards for Vessels of the Armed Forces. Key provisions:

• § 1700.3 — Applicability: covers vessels owned or operated by the Department of Defense and U.S. Coast Guard; the UNDS apply when vessels operate in the navigable waters of the United States and the contiguous zone (3 to 12 nautical miles); beyond 12nm, MARPOL Annexes and related international rules apply
• § 1700.4 — Equipment performance standards: the EPA/DoD UNDS establish whether each of the 25 vessel discharge streams must use a Marine Pollution Control Device (MPCD) — equipment that meets EPA/Navy performance standards — or may be discharged without restriction in most waters; each discharge category in Subpart D has its own status (MPCD required, not required, or prohibited)
• § 1700.10 — No-discharge zones: EPA may establish NDZs for specific armed forces vessel discharge categories in specific waters, where a state petitions and EPA finds that the existing standards are insufficient to protect a designated use; § 1700.11 governs state petitions for NDZs (states must demonstrate that existing UNDS are insufficient)
• § 1700.14 — Aqueous Film Forming Foam (AFFF) firefighting agent: AFFF containing PFAS (per- and polyfluoroalkyl substances) may not be discharged into navigable waters or within 3 nautical miles of the baseline; AFFF discharges are permitted seaward of 3nm only as necessary for emergency firefighting or required training; this prohibition reflects the contamination legacy of AFFF use at military installations, where groundwater and surface water PFAS contamination has created major cleanup liability
• § 1700.15 — Catapult water brake tank effluent: unique to aircraft carriers — the catapult system that launches carrier-based aircraft uses a water brake to decelerate the shuttle at the end of the stroke, generating high-volume contaminated water; carrier catapult effluent may not be discharged in navigable waters or the contiguous zone; aircraft carriers must either retain this effluent or treat it to remove hydraulic fluids and metals before any discharge
• § 1700.16 — Chain locker effluent: when a vessel weighs anchor, seawater and sediment trapped in the chain locker is discharged; Part 1700 allows chain locker washdown discharges but requires that the water be minimized (locker must be pumped before entering port) and that anchor chain sediment accumulation be managed to reduce the discharge of bottom sediment into harbor areas
• § 1700.19 — Controllable pitch propeller (CPP) hydraulic fluid: vessels with CPP systems use hydraulic fluid that can leak through propeller shaft seals into the water; Part 1700 requires that CPP systems minimize hydraulic fluid loss through proper maintenance and seal integrity; ships must track fluid additions and investigate unexplained losses as potential environmental incidents

The UNDS regulations reflect a fundamental tension in military environmental compliance: operational readiness sometimes requires discharges (emergency AFFF use, catapult operations at sea) that would be prohibited in civilian maritime law, while peacetime operations in harbors and near the coast must meet standards comparable to civilian vessel requirements. The AFFF/PFAS prohibition in navigable waters is particularly significant given the scope of documented PFAS contamination at Navy and Air Force installations — over 700 military installations have documented PFAS contamination requiring cleanup, and each training use of PFAS-containing AFFF historically contributed to groundwater plumes.

Recent rulemakings: EPA and DoD have been engaged in ongoing UNDS rulemakings to update performance standards for additional discharge categories and to address PFAS in more categories of military vessel discharges. The 2021–2023 period saw significant PFAS regulatory activity including updated NDZ petitions from coastal states and EPA's own PFAS strategic roadmap affecting Part 1700 AFFF provisions.

How It Affects You

If you work in shipping, maritime operations, or vessel management: MARPOL compliance is both an ethical obligation and a significant legal risk. Oil Record Book falsification is a federal felony — individual chief engineers and officers have received prison sentences for signing false records, even when directed to do so by management. The "directed to falsify" defense has not been successful in federal prosecutions; supervisory direction to commit a crime does not immunize the individual who commits it. For shipping companies: invest in adequate OWS equipment (cheap OWS that clog frequently create pressure to bypass them), adequate bilge reception facilities at all ports of call, robust internal auditing of ORBs, and a compliance culture where crew feel safe reporting problems. The compliance monitor conditions imposed on Carnival (mandatory monitoring on all ships for years) impose enormous ongoing costs — the criminal fine is often less than the total compliance costs. For Annex VI: verify that your bunker suppliers are delivering fuel that meets ECA sulfur requirements; fuel testing is cheap compared to violation penalties, and the liability for burning non-compliant fuel rests with the ship operator even if the supplier delivered non-conforming fuel.

If you live in a port city or coastal community: The North American Emission Control Area (ECA) — requiring 0.10% sulfur fuel within 200 nautical miles of the U.S. coast — has been one of the most consequential clean air improvements in port communities in the last decade. Before the ECA, ships burned "bunker fuel" (heavy fuel oil) with sulfur content up to 3.5%. The health impacts of sulfur dioxide and particulate matter from ships were concentrated in port communities — disproportionately affecting low-income and communities of color near major ports. The 0.10% sulfur ECA requirement, combined with California's more aggressive at-berth requirements (requiring shore power or clean auxiliary generators while docked), has meaningfully improved air quality near major U.S. ports. Local health advocates can track Coast Guard Port State Control enforcement data (published by MARAD and Coast Guard) to monitor compliance rates of vessels calling at their port.

If you are a marine environmental researcher, conservationist, or work in ocean policy: MARPOL Annex V's prohibition on plastic discharge at sea has been global law since 1988 — but enforcement on the open ocean is extremely difficult. Most documented ocean plastic pollution comes not from vessels discarding waste overboard (which is prohibited and criminally enforced at port) but from land-based sources reaching the ocean through rivers and coastal runoff. The practical gap between the legal prohibition and actual ocean plastic levels illustrates a core challenge of international maritime environmental law: standards are set multilaterally (IMO), enforcement is delegated to flag states (often with weak enforcement capacity) and port states (only in port), and open-ocean enforcement is nearly non-existent. The IMO's GHG reduction framework (EEXI and CII) is the next frontier — the first globally binding emissions reduction system for an entire industry sector, with significant implications for shipping economics, vessel values, and fuel technology investment. U.S. position in IMO GHG negotiations has been an important but often underappreciated element of international climate policy.

State Variations

MARPOL is a federal matter implemented through APPS, but state law interacts in several ways:

• California's at-berth regulations: California requires vessels berthed at California ports to use shore power (cold ironing) or equivalent clean energy while docked, going beyond MARPOL Annex VI requirements. This state regulation has driven shore power infrastructure investment at California ports and has been a model for other port communities.
• Clean Water Act § 312 (marine sanitation devices): States can designate "No Discharge Zones" (NDZs) for vessel sewage under CWA § 312, requiring vessels in those zones to use Type III Marine Sanitation Devices (holding tanks) regardless of MARPOL Annex IV standards. Many states have designated NDZs in sensitive waters (harbors, estuaries, near shellfish beds). Vessel operators must know which waters are NDZs.
• State reception facilities: Port states (including U.S. port authorities and state agencies) must provide adequate reception facilities for vessel waste (oily bilge water, sewage, garbage). Inadequate facilities are themselves an MARPOL compliance issue and drive illegal disposal.

Recent Developments

• 2020 — IMO 2020 global sulfur cap: The global maritime sulfur limit dropped from 3.5% to 0.50% on January 1, 2020 ("IMO 2020"), the most significant change to shipping economics in years. Vessel operators had to choose between: (a) switching to low-sulfur fuel (significantly more expensive), (b) installing scrubbers (exhaust gas cleaning systems) to continue using cheaper high-sulfur fuel while reducing sulfur emissions, or (c) converting to LNG propulsion. The Coast Guard has been actively sampling bunker fuel to verify compliance.
• 2023 — GHG regulation enters force: IMO's EEXI (Energy Efficiency Existing Ship Index) and CII (Carbon Intensity Indicator) regulations entered force, requiring ships to demonstrate energy efficiency and rate their carbon intensity annually. Ships rated E for three consecutive years must develop corrective action plans. This is the beginning of a binding GHG reduction framework for international shipping.
• 2024 — FuelEU Maritime (EU context): The European Union enacted its own vessel GHG regulation (FuelEU Maritime) that goes beyond IMO requirements for ships calling at EU ports, including a requirement to use green fuels and a lifecycle GHG accounting framework. U.S.-flag vessels and foreign vessels calling at EU ports will be subject to FuelEU Maritime — creating a new compliance layer beyond APPS/MARPOL.
• 2025 — Coast Guard MARPOL enforcement: The Coast Guard maintained active Port State Control and criminal referral programs for MARPOL violations, with several new cases involving Annex VI (sulfur) violations and continued monitoring of cruise line compliance under active probation programs.
• 2025 — Ammonia and methanol as shipping fuels: The maritime industry's search for low-carbon fuels drove investment in ammonia (zero carbon when made from green hydrogen) and methanol as bunker fuel alternatives. IMO updated its Interim Guidelines for ships using methanol as fuel; ammonia guidelines are in development. These emerging fuels create new safety and pollution prevention challenges that MARPOL's current annexes were not designed to address.