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

State Program Contact

Illinois EPA Surface Water Monitoring Exit

Water Quality Standards

WQS Information
The link to Illinois' WQS that are in effect for Clean Water Act purposes is provided. These are the WQS approved by EPA.
  • Water Quality Standards Regulations: Illinois
The state of Illinois 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
The following Aquatic Life Uses (ALU) represent at least three different levels of potential biological condition. General Use and Upper Dresden Island Pool ALU represent biological condition consistent with the “balanced indigenous populations” aquatic-life goal of the Clean Water Act.

  • General Use
  • Upper Dresden Island Pool ALU
  • Chicago Area Waterway System ALU A
  • Chicago Area Waterway System and Brandon Pool ALU B
  • Indigenous ALU (South Fork South Branch Chicago River only)

Biological Criteria
_____ Narrative
_____ Numeric
__X__ No criteria

Antidegradation Policy
Title 35: Subtitle C, Chapter 1, Part 302, Subpart A, Section 302.105 - Antidegradation of the Illinois Administrative Code

Biological Assessment

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

Are bioassessments used to support 303(d) listings? 
Yes. Listing methodology: Integrated Water Quality Report and 303d Lists

How are assemblages used to make impairment decisions?
Each are applied independently

Other uses of biocriteria or bioassessment within the water quality program:
Refining ALU, TMDL development and assessment, antidegradation, non-point source assessments, 305(b) surface water condition assessments, and evaluation of discharge permit conditions.

Technical Support Information and Documents:

Reference condition:
Illinois fish and macroinvertebrate biological indexes represent a measure of similarity to/dissimilarity from the expected least-disturbed biological condition that best pertains to the site being assessed.

Not applicable.

Stressor identification/causal analysis approach:
Water chemistry and physical habitat are measured or otherwise assessed at the time of biological sampling.

Technical reference material:
Integrated Water Quality Report and 303d Lists

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