Great Lakes Water Quality Guidance

The Great Lakes contain approximately 21 percent of the world's surface freshwater and supply drinking water to over 30 million people. Congress recognized this exceptional resource warrants its own federal water quality floor. 40 CFR Part 132 — the "Water Quality Guidance for the Great Lakes System" — establishes minimum water quality standards, antidegradation policies, and implementation procedures that all eight Great Lakes states and tribes must adopt in their own programs. It is the only region-specific federal water quality standard in the United States.

Legal Authority

• 33 U.S.C. § 1251 — Clean Water Act § 118(c)(2) (Great Lakes Critical Programs Act of 1990, Pub. L. 101-596); directs EPA to publish water quality guidance for the Great Lakes System specifying minimum water quality standards, antidegradation policies, and implementation procedures; requires Great Lakes states to adopt standards consistent with the guidance
• 33 U.S.C. § 1313 — Clean Water Act § 303; state water quality standards authority; the framework under which states set standards and EPA approves or disapproves; Part 132 sets a federal floor that state standards in the Great Lakes basin must meet
• 40 CFR Part 132 — EPA's Great Lakes Water Quality Guidance; establishes numeric water quality criteria for bioaccumulative chemicals of concern (BCCs), mixing zone policies, antidegradation policies, and variances applicable throughout the Great Lakes System

Key Mechanics

40 CFR Part 132 establishes the only region-specific federal water quality standard in the U.S., applying to the five Great Lakes and all tributaries within the eight Great Lakes states' portions of the basin. The rule's most distinctive feature is its treatment of bioaccumulative chemicals of concern (BCCs) — pollutants like PCBs, dioxins, and mercury that accumulate in fish tissue and persist in the aquatic food web. For BCCs, Part 132 generally prohibits mixing zones (the dilution area where effluent mixes with receiving water) — an approach more stringent than standard CWA practice, which allows mixing zones for most pollutants. This reflects the Great Lakes' unique ecological risk: biomagnification through the food chain means that even diluted BCC concentrations in water translate to elevated concentrations in fish tissue consumed by humans. States must adopt numeric water quality criteria, antidegradation policies (protecting existing high-quality waters), and implementation procedures consistent with Part 132 Appendices — or EPA can promulgate standards directly. NPDES permits for Great Lakes dischargers must include effluent limits that achieve Part 132 standards. EPA reviews state program consistency and may withdraw approval if states adopt standards that do not meet the guidance's requirements.

Current Rule (2026)

What This Rule Does

40 CFR Part 132 requires the eight Great Lakes states and affiliated tribes to adopt water quality standards and implementation procedures that are at least as protective as the minimum standards in this part. State programs do not need to be identical to the Guidance, but must contain provisions consistent with (meaning at least as protective as) the Guidance. EPA reviews state adoptions and can require revisions if a state's program falls below the Guidance floor.

The Guidance establishes four sets of numeric water quality criteria (Tables 1–4), methodologies for deriving those criteria, an antidegradation policy, and detailed implementation procedures for translating criteria into NPDES permit limits.

Key Provisions

• § 132.1 — Scope: establishes this part as the Water Quality Guidance required by CWA § 118(c)(2) as amended by the Great Lakes Critical Programs Act of 1990; identifies the scientific basis documents (preamble, Technical Support Documents) that explain each provision
• § 132.2 — Definitions: specialized terms include Bioaccumulation Factor (BAF) (ratio of a substance's concentration in tissue to its concentration in ambient water, accounting for all routes of exposure including food chain uptake), Acute-Chronic Ratio (ACR) (measure of relationship between acute and chronic toxicity used to derive chronic criteria from acute data), and Tier I/Tier II methodology (higher-confidence vs. lower-confidence procedures for deriving criteria)
• § 132.3 — Adoption of criteria: Great Lakes states and tribes must adopt numeric water quality criteria consistent with: Table 1 (acute aquatic life criteria), Table 2 (chronic aquatic life criteria), Table 3 (human health criteria), and Table 4 (wildlife criteria) — or site-specific modifications meeting Procedure 1 of Appendix F
• § 132.4 — State adoption of methodologies: states and tribes must adopt requirements consistent with the Guidance's Appendices A (aquatic life methodology), B (bioaccumulation factors), C (human health methodology), D (wildlife methodology), E (antidegradation policy), and F (implementation procedures)
• § 132.5 — Procedures for adoption and EPA review: states must have submitted initial Guidance-consistent standards to EPA; EPA reviews state programs and may require revisions; states that have not adopted consistent standards are subject to EPA promulgation (federal standards replace state standards for Great Lakes waters)
• § 132.6 — State-specific applications: several provisions became effective at different dates for specific states (Indiana, Illinois, New York, Ohio, Michigan) based on litigation and negotiated compliance schedules from 2000–2001

The Four Sets of Criteria (Tables 1–4)

Table 1 — Acute Aquatic Life Criteria: the concentration of each chemical that should not be exceeded more than once every 3 years on average to protect aquatic organisms from acute toxicity; expressed as 1-hour average concentrations; covers metals (arsenic, cadmium, chromium, copper, lead, mercury, nickel, zinc), pesticides (chlordane, dieldrin, endrin, lindane), and industrial chemicals (PCBs, dioxin equivalents, polycyclic aromatics)

Table 2 — Chronic Aquatic Life Criteria: concentrations that should not be exceeded more than once every 3 years on average for chronic (long-term) effects; typically 1/10th to 1/100th of the acute criterion; bioaccumulative chemicals that concentrate in the food chain (PCBs, dioxin, chlordane) are regulated at sub-ppb levels

Table 3 — Human Health Criteria: criteria derived to protect people who consume Great Lakes fish and water, based on cancer risk (10⁻⁵ to 10⁻⁶ risk level) for carcinogens and reference doses for non-carcinogens; the critical pathway is fish consumption — the Guidance uses higher fish consumption rates than the national criteria (0.0175 kg/day rather than the previous 0.0065 kg/day) reflecting the actual Great Lakes fish-eating populations; highly bioaccumulative substances like dioxin, PCBs, and mercury are regulated at extremely low concentrations

Table 4 — Wildlife Criteria: criteria protective of wildlife species (fish-eating birds like bald eagles, ospreys, great blue herons; fish-eating mammals like mink, river otter) that are at the top of the Great Lakes food chain and concentrate pollutants through bioaccumulation; driven by dioxin, PCBs, mercury, chlorinated pesticides; the wildlife criteria are often more stringent than human health criteria for the most bioaccumulative substances

Antidegradation (Appendix E)

The Great Lakes antidegradation policy mirrors and strengthens the national antidegradation requirements (40 CFR § 131.12) for the Great Lakes System. Outstanding National Resource Waters in the basin cannot receive additional degradation. High-quality waters can only be degraded for significant social and economic benefit after demonstration that less degrading alternatives are not available.

How It Affects You

NPDES permittees discharging to Great Lakes tributaries — permit limits in Great Lakes states are often more stringent than in other states, particularly for metals, dioxins, PCBs, and mercury, reflecting the Guidance's criteria and bioaccumulation-driven fish consumption standards; facilities near the Great Lakes should expect stricter effluent limits for bioaccumulative pollutants

Tribes — several federally recognized tribes in the Great Lakes basin exercise treaty rights to fish and other resources; tribal water quality standards under the Guidance protect these treaty uses; some tribal standards are stricter than state standards for mercury and dioxin

Anglers and fish consumption advisories — the Wisconsin, Michigan, Minnesota, Ohio, and other state advisories limiting consumption of Great Lakes fish species (lake trout, salmon, walleye) are driven by contaminant concentrations that exceed the Guidance's human health criteria

Statutory Authority

This rule implements:

• 33 U.S.C. § 1251 and specifically CWA § 118(c)(2) — directs EPA to publish guidance containing minimum water quality standards for the Great Lakes System; amended by Great Lakes Critical Programs Act of 1990

Recent Rulemakings

• 76 FR 57652 (Sept. 15, 2011) — clarification amendments to Appendix F implementation procedures (wasteload allocation methodology)
• 65 FR 67650 (Nov. 13, 2000) — major amendments to Appendix F implementation procedures
• Original promulgation: 60 FR 15387 (March 23, 1995)

Pending Action

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