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

State Program Contact

Montana Department of Environmental Quality Exit

Water Quality Standards

WQS Information
The link to Montana's WQS that are in effect for Clean Water Act purposes is provided. These are the WQS approved by EPA.
The state of Montana 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

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Designated Aquatic Life Uses
Two use categories – warm water versus cold water fishes

  • Growth and propagation of salmonid fishes and associated aquatic life
  • Growth and propagation of non-salmonid fishes and associated aquatic life

Biological Criteria
_____ Narrative
_____ Numeric
__X__ No criteria

Antidegradation Policy
Use of biocriteria or bioassessments not included in antidegradation policy

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: Assessment Methodology for Determining Wadeable Stream Impairment Due to Excess Nitrogen and Phosphorus Levels (PDF) (83 pp, 2 MB)
The Montana Department of Environmental Quality Western Montana Sediment Assessment Method: Considerations, Physical and Biological Parameters, and Decision Making (PDF) (70 pp, 2 MB)
Montana’s DEQ Standard Operating Procedures

How are assemblages used to make impairment decisions?
Biological assemblages are used as primary or secondary indicators depending on the assessment method. Overall, a weight approach is used in the nutrient and sediment assessment methods.

Other uses of biocriteria or bioassessment within the water quality program:
Criteria development and criteria refinement

Technical Support Information and Documents:

Reference condition:
A detailed explanation can be found in the document listed below. Briefly, there are 2 tiers for reference site definitions and characterization.

  • Tier 1 – Natural condition: The characteristics of a waterbody that is unaltered from its natural state, or there are no detectable human-caused changes. This is the highest attainable biological, chemical, physical and riparian conditions for waterbodies
  • Tier 2 – Minimally Impacted condition: The characteristics of a waterbody in which the activities of man have made small changes. Minimally impacted conditions can be used to describe attainable biological, chemical, physical and riparian habitat conditions for waterbodies with similar watershed characteristics within similar geographic regions and represent the water body’s best potential condition.

The identification criteria (cold water versus warm water) is based on two categories:

  • Physical Habitat (road densities, new and old timber harvests, % surface fines, sediment deposition, bank erosion and vegetation, permitted point sources, grazing use, mining activity, agricultural use, oil and gas activity)
  • Best Professional Judgment (anecdotal evidence from non-standard sources, field observations not listed as criteria, aesthetics, and other determinations

Technical reference material: 
Identification and Assessment of Montana Reference Streams: A Follow-up and Expansion of the 1992 Benchmark Biology Study (PDF) (49 pp, 922 K)

Not applicable.

Stressor identification/causal analysis approach:
Response signatures - Diatom based metrics to determine if an impairment is caused by sediment or nutrients. Macroinvertebrates are used in a general biological integrity.

Technical reference material: 
Diatom Biocriteria for Montana Streams (PDF) (26 pp, 1 MB)

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