Triennial Review of Maine's Water Quality Standards- 2024 through 2026


Maine's water quality standards describe what uses, such as recreation or fishing, are appropriate for which waterbodies, and which criteria and antidegradation measures are in place to protect those uses. More information on Maine's water quality standards can be accessed on DEP's Water Quality Standards page, which provides links to existing Maine statutes and rules.

The federal Clean Water Act (§303(c)(1); 40 CFR Part 131.20 - federal rules, off-site) requires that states periodically, but at least once every 3 years, hold public hearings for the purpose of reviewing water quality standards and, as appropriate, modifying and developing standards. This process is known as the Triennial Review. Maine Statute contains similar language in 38 M.R.S.§464.3.B.

The Department concluded the most recent Triennial Review in 2022. In March 2024, the Department initiated a new Triennial Review, which is expected to extend into 2026 for any required legislation. To start the process, on March 18, 2024 a request to submit proposals on changes to Maine’s water quality standards was sent to recipients at Non-Governmental Organizations, municipalities, tribes, state and federal agencies, etc., and to subscribers to the Department’s subscription list for Opportunity for Comment. Submission guidelines (pdf) including a timetable were included in the mailings.

Over the course of the Review, the Department will evaluate all proposals received and develop draft recommendations for proposed changes. Opportunities for public comment will be offered by the Department and the Board of Environmental Protection. Public comment may also be submitted when the final draft recommendations are before the Maine Legislature as the institution responsible for making statutory changes. Ultimately, the U. S. Environmental Protection Agency must give final approval to any changes made by the State of Maine.

Proposals for Updates to Maine Water Quality Standards

The Department received proposals to change water quality standards, including water quality classifications, from the U.S. Environmental Protection Agency (USEPA) and stakeholders, and also developed its own proposals as detailed below.

Proposals for updates to water quality standards (WQS). The USEPA and five stakeholders submitted proposals:

  • USEPA (pdf)
    • Update regulations for surface water quality criteria for toxic pollutants relating to the protection of aquatic life (aluminum, copper, selenium; ambient water physical characteristics; small corrections on ammonia and arsenic).
    • Add freshwater and estuarine/marine pH criteria to fresh surface waters, lakes and ponds, and estuarine and marine waters.
    • Correct equation used for calculating Secchi Disk Trophic State Index.
    • Expand existing recreational WQS for Class GPA by adopting federal standards for cyanotoxins.
    • Update recreational water quality criteria for Classes B, C, SB and SC to be applicable year-round.
    • Expand regulations relating to water temperature in tidal waters.
    • Eliminate applicability of natural conditions clause to water quality criteria intended to protect human health (toxics, bacteria).
    • Expand mixing zone policy related to discharges.
  • Androscoggin River Watershed Council (pdf)
    • Create a new water quality class by renaming the current ‘Class B’ with existing standards to ‘Class BB’. Maintain the existing ‘Class B’ classification but update the dissolved oxygen criteria with less stringent standards (pdf pages 1-2 and 6).
    • Provide a limited exemption for topographic areas regarding measurement of dissolved oxygen in riverine impoundments (pdf pages 5-6).
  • Conservation Law Foundation (pdf)
    • Prohibition on discharges that impart odor.
    • Expand descriptors for general condition of surface waters.
    • Specify dissolved oxygen criteria for Class AA and SA waters.
    • Amend dissolved oxygen criteria for Class A and B waters.
  • Frenchman Bay United (pdf)
    • Amend and expand finfish aquaculture permitting provisions.
  • Friends of Casco Bay (pdf)
    • Amend dissolved oxygen criteria for Class A and B waters.
    • Add narrative nitrogen criteria to Class SA and SB waters.
  • Hancock County Soil & Water Conservation District

The Department developed 2 proposals (pdf):

  • Clarify aquatic life standards for Class GPA (lakes and ponds) waters.
  • Update dissolved oxygen criteria in Class B (fresh surface waters) waters.

Proposals for upgrades of water quality classifications. Six stakeholders submitted proposals (numbers refer to items in the map below):

  • Androscoggin River Watershed Council (pdf) (pages 3-6)
    • (3) Upgrade to Class B: Androscoggin River from confluence with Ellis River to Worumbo Dam in Lisbon Falls (Rumford, Mexico, Peru, Dixfield, Canton, Jay, Livermore Falls, Livermore, Turner, Leeds, Greene, Auburn, Lewiston, Lisbon, Durham).
  • Eastern Maine Conservation Initiative (pdf)
    • (4) Upgrade to Class SA: Chandler Bay (Jonesport).
  • Friends of the Presumpscot River and American Rivers (pdf)
    • (7) Upgrade to Class B: Presumpscot River from Saccarappa Falls to Head of Tide at Presumpscot Falls (Westbrook, Portland, Falmouth).
    • Letter of support is available on request.
  • Grow L+A (pdf)
    • (2) Upgrade to Class B: Androscoggin River from the base of Gulf Island Pond to Worumbo Dam in Lisbon Falls (Auburn, Lewiston, Durham, Lisbon).
  • Hancock County Soil & Water Conservation District (pdf)
    • (11) Upgrade to Class AA: West Branch, Middle Branch, and East Branch Union River (Great Pond, Amherst, Aurora, Mariaville, Osborne, T22 MD, Waltham) and associated tributaries (overlapping and adjacent towns).
  • Midcoast Conservancy (pdf)
    • (9) Upgrade to Class A: Sheepscot River from Somerville/Palermo town line downstream to Route 17 in Whitefield (Windsor, Somerville, Whitefield, Jefferson).

The Department developed five proposals (pdf) (numbers refer to items in the map below):

  • (1) Upgrade to Class AA: Abbott Brook and one unnamed tributary (Parkertown TWP)
  • (5) Upgrade to Class AA: Mount Blue Stream and tributaries (Weld, Avon)
  • (6) Upgrade to Class AA: Pleasant River, Middle Branch and tributaries (Brownville, Williamsburg, Ebeemee TWP, Katahdin Iron Works TWP, and TB R11 WELS)
  • (8) Upgrade to Class A: Sandy River and tributaries (Strong, Avon, Freeman Twp., Phillips, Temple, New Vineyard, Weld)
  • (10) Upgrade to Class A: Temple Stream and tributaries (Avon, Temple, Wilton, and Farmington)
Figure 1. Overview Map Showing Locations of Proposals for Classification Upgrades
Key Segment Current Class Proposed Class
1 Abbott Brook, one unnamed tributary A AA
2 Androscoggin River (base of Gulf Island Pond to Worumbo Dam) C B
3 Androscoggin River (confluence with Ellis River to Worumbo Dam) C B
4 Chandler Bay SB SA
5 Mount Blue Stream and tributaries A AA
6 Pleasant River, Middle Branch and tributaries A AA
7 Presumpscot River (Saccarappa Falls to Head of Tide at Presumpscot Falls) C B
8 Sandy River and tributaries B A
9 Sheepscot River (Rt. 17 crossing/Whitefield to Somerville/Palermo townline) B A
10 Temple Stream and tributaries B A
11 Upper Union River: West Branch, Middle Branch, East Branch and associated tributaries A AA

Statutory clarifications. The Department also proposes to amend three statutory sections as follows:

  • Designated use clarification
    • In 38 M.R.S. Section 465-B.3.A. (designated use section for Class SC), add the phrase shown with underline: “A. Class SC waters must be of such quality that they are suitable for the designated uses of recreation in and on the water, fishing, aquaculture, propagation and restricted harvesting of shellfish, industrial process and cooling water supply, hydroelectric power generation, navigation and as a habitat for fish and other estuarine and marine life.”
  • Location clarification
    • In 38 M.R.S. Section 467.7.F.5., add an alternative road name as shown with underline: “Olamon Stream and its tributaries above the bridge on Horseback Road/Spring Bridge Road - Class A.”
  • Waterbody name clarification
    • In 38 M.R.S. Sections 467.4.H.2.a., add the alternative names shown in parentheses: “Sebasticook River, East Branch from the outlet of Corundel Lake (also known as East Branch Sebasticook River Reservoir, and Corundel Bog) to its confluence with the West Branch - Class C.”


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