An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Bioassessment and Biocriteria Program Status for Wyoming: Streams and Wadeable Rivers

State Program Contact

Wyoming Department of Environmental Quality Exit

Water Quality Standards

WQS Information
The link to Wyoming's WQS that are in effect for Clean Water Act purposes is provided. These are the WQS approved by EPA.
The state of Wyoming provided information and links to sections of their administrative code on designated aquatic life use, biological criteria, antidegradation as well as technical support documents and information on its bioassessment and biocriteria programs. These are included for your convenience and may or may not reflect the most recently EPA approved WQS. The following links exit the site Exit

You may need a PDF reader to view some of the files on this page. Refer to EPA’s about PDF page to learn more.

Designated Aquatic Life Uses
Wyoming’s ‘aquatic life’ uses are represented by two designated uses: 1) Fisheries, where levels of protection are subdivided into cold, warm and non-game fisheries; and 2) Aquatic Life other than Fish where benthic macroinvertebrates are used as the primary biotic community indicator
  • Fisheries – Cold Water Game
  • Fisheries – Warm Water Game
  • Fisheries – Non Game
  • Aquatic life other than fish

Biological Criteria
__X__ Narrative, with quantitative implementation procedures or translators (refer to Biological Assessment)
_____ Numeric
_____ No criteria

Section 32. Biological Criteria. Class 1, 2 and 3 waters of the state must be free from substances, whether attributable to human-induced point source discharges or nonpoint source activities, in concentrations or combinations which will adversely alter the structure and function of indigenous or intentionally introduced aquatic communities.

Section 28. Undesirable Aquatic Life. All Wyoming surface waters shall be free from substances and conditions or combinations thereof which are attributable to or influenced by the activities of man, in concentrations which produce undesirable aquatic life.

Antidegradation Policy
Biocriteria are not used to implement antidegradation policies.

Biological Assessment

What biological assemblages are used in the bioassessment program?
Benthic macroinvertebrates and periphyton

Are bioassessments used to support 303(d) listings?
Yes. Listing methodology: Wyoming’s Methods for Determining Surface Water Quality Condition and TMDL Prioritization (PDF) (22 pp, 548 K)

How are assemblages used to make impairment decisions?
Wyoming’s WSII and WYRIVPACS are used as part of the weight of evidence approach to evaluate narrative criteria (Sections 28 and 32) associated with the aquatic life other than fish designated use in the state’s perennial wadeable streams. These models use benthic macroinvertebrates as the primary aquatic indicator. Results of the two models are combined into a single narrative rating and incorporated (along with findings from the periphyton assemblage as a supplemental aquatic indicator) into a weight-of-evidence evaluation of the aquatic life other than fish use support. Wyoming often uses the aquatic life other than fish designated use determinations as a surrogate measure of fisheries designated use support.

Technical reference material:
Wyoming RIVPACS (WYRIVPACS) (PDF) (84 pp, 4 MB)
Wyoming Stream Integrity Index (WSII) (PDF) (108 pp, 6 MB)

Other uses of bioassessment within the water quality program:
TMDL development and assessment, non-point source assessments, BMP evaluation, 305(b) surface water condition assessments, and restoration goals.

Technical Support Information and Documents:

Reference condition:
Wyoming has a reference network consisting of over 200 sites identified between 1992 and the present and distributed across six level III ecoregions. This network represents predominantly wadeable perennial streams and rivers.

Technical reference material:
Wyoming uses the Reach and Watershed Characterization Checklist as an initial screening tool to identify candidate reference sites. This checklist can be found in the Monitoring Procedure Sequence SOP (PDF) (307 pp, 6 MB).

Findings from this checklist in addition to other abiotic and watershed information are used in a weight-of-evidence approach to ascertain the suitability of a site as reference.

Refer to section on Biological Assessment.

Stressor identification/causal analysis approach:
Stressor identification and causal analyses may be employed within the context of Wyoming’s weight-of-evidence approach to assess the designated use support of surface waters. Refer to Wyoming’s listing methodology for a description of Wyoming’s weight-of-evidence approach. CADDIS or other formalized procedures are not used. Stressor identification and causal analysis are linked by paired biota and stressor monitoring; evaluation of response signatures.

Top of Page