Maine's Water Quality Standards


Section 303(c) of the federal Clean Water Act (CWA) as implemented in 40 CFR Part 131 (federal rules, off-site) requires all States to develop and maintain Water Quality Standards. These standards describe the intended uses of a waterbody, for example recreation in and on the water, fishing, and as habitat for aquatic organisms. Standards also include narrative or numeric criteria and an antidegredation policy that ensures that those uses can be achieved.

This page is intended to provide a general listing of Maine's "water quality standards", as this phrase is used by the Maine DEP's water quality and assessment program in considering ambient water quality, as well as the waste discharge licensing program. These standards are one of the principal foundations for the protection of water quality in Maine.

A majority of these standards are also part of the water quality "docket" of standards that is maintained with the U.S. Environmental Protection Agency (USEPA). Changes to docket standards require the approval of the USEPA for purposes of implementation of the federal Clean Water Act. See the Docket Page for more information on docket standards. See also Water Quality Standards, 40 CFR Part 131 (federal rules) (off-site).

Note that a number of other laws administered by the DEP help to maintain, restore and protect water quality in Maine. Some of these laws provide requirements specific to activities in certain locations, such as activities in or close to protected natural resources (see Natural Resources Protection Act). Some provide additional requirements specific to certain types of activity with significant potential impacts, such as mining, activities disturbing one or more acres (Stormwater Management Law. and the large developments regulated under Maine's Site Location Law. The short and basic requirements of the Erosion and Sedimentation Control Law mean that activities that don't otherwise need a permit should still include measures to prevent unreasonable erosion.

According to the federal Clean Water Act, states are required to periodically, but at least once every three 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. The DEP conducted its last Triennial Review between January 2020 and December 2021, and initiated a new Triennial Review in March 2024. For further information, please visit the Triennial Review webpage.

Statute (off-site links)

  • The following sections are from Article 1, Organization and General Provisions
  • The following sections are from Article 1-F, Nonpoint Source Pollution Program
  • The following sections are from Article 3, Pollution Control
  • The following sections are from Article 3, Enforcement
  • The following sections are from Article 4-A, Water Classification Program
  • Approval criteria, 38 MRS 636 (hydropower projects)

Rules (off-site links)


Related on-site links