Water Quality Standards Regulations: Idaho

Presented are water quality standards in effect for Clean Water Act (CWA) purposes for this state.

The EPA is posting these standards as a convenience to users and has made a reasonable effort to assure their accuracy. For each document listed under "State Standards in Effect for CWA Purposes", the EPA has made a reasonable effort to identify parts of the standards that are disapproved or are otherwise not in effect for CWA purposes. Additionally, please note the documents may also contain provisions that the EPA does not have the authority and duty to act on under the Clean Water Act because the provisions are not water quality standards.

• What is a New or Revised Water Quality Standard Under CWA 303(c)(3)? - Frequently Asked Questions (pdf) (108.04 KB)

• State Standards in Effect for CWA Purposes
• Federally Proposed or Promulgated Standards

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• State Standards in Effect for CWA Purposes
• Federally Proposed or Promulgated Standards
• Selected Actions and Correspondence

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State Standards in Effect for CWA Purposes

• Idaho Water Quality Standards (pdf) (3.67 MB)
  (Effective September 29, 2023) State regulation establishing water quality standards for surface waters of the state.  Please note that not all parts of this document are effective for Clean Water Act purposes. Refer to cover pages for more information.

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Federally Proposed or Promulgated Standards

• 40 CFR §131.33  Idaho

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Selected Actions and Correspondence

Recent actions along with supporting documents are provided for reference.

• EPA Review and Action on Idaho’s Revised Human Health Criteria for Arsenic (pdf) (519.47 KB)

• EPA Review and Action on Revised Recreational Bacteria Criteria (pdf) (323.94 KB)

• EPA Action on Idaho’s Revised Water Quality Standards, Bull Trout Spawning and Rearing Temperature Criteria (pdf) (152.1 KB)

• EPA Review and Action on Idaho’s Water Quality Standards, Seasonal Cold Water Criteria (pdf) (7.53 MB)

• EPA Review and Action on Idaho's New and Revised Water Quality Standards, Mixing Zone Policy (pdf) (1.19 MB)

• EPA Review and Action on Idaho's Revised Site-Specific Criteria for Temperature for the Hells Canyon Reach of the Snake River (pdf) (648.48 KB)

• Approval and Disapproval of Selenium Aquatic Life (pdf) (2.03 MB)

• Approval of Idaho’s Copper Aquatic Life Criteria based on the Biotic Ligand Model (pdf) (1.35 MB)
• Implementation Guidance for the Idaho Copper Criteria for Aquatic Life (pdf) (2.18 MB)

• EPA's April 4, 2019 Action on Idaho's Updated Human Health Criteria (pdf) (1.66 MB)