Water Quality Standards Regulations: Colorado

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

• The Basic Standards and Methodologies for Surface Water, Regulation No. 31 (pdf) (9.02 MB)
  (Effective November 25, 2024) This regulation provides basic water quality standards, an antidegradation rule and implementation process, and a system for classifying state surface waters, for assigning water quality standards, for granting temporary modifications, and for periodic review of the classifications and standards. Please note that not all parts of this document are effective for Clean Water Act purposes. Refer to cover pages for more information.
• Colorado River Salinity Standards, Regulation No. 39 (pdf) (516.65 KB)
  The regulation establishes water quality standards for salinity in the Colorado River Basin.
• Water Quality Standards for Salinity - Colorado River System, June 1999 (pdf) (6.91 MB)
• Water Quality Standards for Salinity - Colorado River System, October 1999 (pdf) (2.72 MB)

Classifications and Numeric Standards

The following regulations provide classifications and numeric water quality criteria for the indicated rivers and basins.

• Classifications and Numeric Standards for Arkansas River Basin, Regulation No. 32 (pdf) (11.47 MB)
  (Effective November 25, 2024)
• Classifications and Numeric Standards for Upper Colorado River Basin and North Platte River, Regulation No. 33 (pdf) (11.23 MB)
  (Effective November 25, 2024)
• Classifications and Numeric Standards for San Juan River and Dolores River Basins, Regulation No. 34 (pdf) (8.67 MB)
  (Effective November 25, 2024)
• Classifications and Numeric Standards for San Juan Gunnison and Lower Dolores River Basins, Regulation No. 35 (pdf) (10.12 MB)
  (Effective November 25 2024)
• Classifications and Numeric Standards for Rio Grande Basin, Regulation No. 36 (pdf) (8.03 MB)
  (Effective November 25, 2024)
• Classifications and Numeric Standards for Lower Colorado River Basin, Regulation No. 37 (pdf) (8.22 MB)
  (Effective November 25, 2024)
• Classifications and Numeric Standards for South Platte River Basin, Laramie River Basin, Republican River Basin, Smoky Hill River Basin, Regulation No. 38 (pdf) (17.83 MB)
  (Effective November 25, 2024)

Colorado's water quality standards are applicable to "waters of the State". In some limited instances, the definition adopted by Colorado for "waters of the State" as part of its water quality standards may result in water quality standards that are more comprehensive than required under section 303(c) of the Clean Water Act and the implementing federal regulations. The EPA has included the State's water quality standards in their entirety here for context and as supplementary information for the reader.

Colorado water quality standards apply to all waters within the State of Colorado, with the exception of those waters that are within Indian Country, as defined in 18 U.S.C. Section 1151.

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Federally Proposed or Promulgated Standards

• None at this time.