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

State Program Contact

Iowa Department of Natural Resources Water Quality Exit

Water Quality Standards

WQS Information
The link to Iowa's WQS that are in effect for Clean Water Act purposes is provided. These are the WQS approved by EPA.
The state of Iowa 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
Iowa has five ALU categories that are based on differences in stream size, flow characteristics, thermal regime (i.e., coldwater/warmwater), and capability to sustain game fish populations.

  • Class B(WW-1) – Typically large interior and border rivers and the lower segments of medium-size tributary streams capable of supporting and maintaining a wide variety of aquatic life, including game fish.
  • Class B(WW-2) – Typically smaller, perennially flowing streams capable of supporting and maintaining a resident aquatic community, but lack the flow and habitat necessary to fully support and sustain game fish populations.
  • Class B(WW-3) – Intermittent stream with non-flowing perennial pools capable of supporting and maintaining a resident aquatic community in harsher conditions. These waters lack the flow and habitat necessary to fully support and sustain a game fish population.
  • Class B(CW-1) – Waters in which the temperature and flow are suitable for the maintenance of a variety of cold water species, including reproducing and non-reproducing populations of trout (Salmonidae family) and associated aquatic communities.
  • Class B(CW-2) – Waters that include small, channeled streams, headwaters, and spring runs that possess natural cold water attributes of temperature and flow. These waters usually do not support consistent populations of trout (Salmonidae family), but may support associated vertebrate and invertebrate organisms.

Biological Criteria
_____ Narrative
_____ Numeric
__X__ No criteria

Antidegradation Policy
Biological assessment data can be and have been used to support nominations for Antidegradation Tier 21/2 “Outstanding Iowa Waters”; refer to pages 7-8 of Iowa's Antidegradation Implementation Policy (2-17-10)

“The surface water is of exceptional ecological significance because of its unique attributes as demonstrated through detailed aquatic community assessments, population surveys, or other data available to the department.”

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: visit Iowa DNR's updated assessment and listing methodology refer to "Guidelines for Determining Section 305(B) Aquatic Life Use Support (ALUS) using Stream Biocriteria Sampling Data for the Section 305(b) Reporting and Section 303(d) Listing Cycles" on pages 55-63.

How are assemblages used to make impairment decisions?
For warmwater streams, scores of the Benthic Macroinvertebrate Index of Biotic Integrity (BMIBI) and the Fish Index of Biotic Integrity (FIBI) are individually compared against the applicable Biological Impairment Thresholds (BIT) that is based on ecoregion location and, within certain ecoregions, benthic macroinvertebrate gear type or stream habitat type. The BMIBI and FIBI scores are applied independently. Failure to attain either the BMIBI-BIT or the FIBI-BIT is sufficient basis for impairment listing. To be considered a “Monitored” bioassessment and eligible for Section 303(d) listing, valid scores of the BMIBI and/or FIBI must be available from at least two years of the five-year data evaluation period included in the current 305(b)/303(d) Integrated Report cycle. Additionally, the warm water streams must have watershed areas in the calibrated range of the wadeable reference sites. The Coldwater Benthic (macroinvertebrate) Index (CBI) is applied in a similar way for bioassessment of streams designated for coldwater aquatic life uses.

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 restoration goals

Technical Support Information and Documents:

Reference condition:
Iowa currently has a network of 89 warmwater and 15 coldwater contemporary least disturbed reference sites for wadeable, perennial streams. The bioassessment program is also evaluating candidate least disturbed reference sites for small, headwater streams having perennial flow or perennial pooled habitat. Candidate reference sites are identified based on a GIS analysis of watershed characteristics and further evaluated through field reconnaissance.

Technical reference material:
The approach used to establish reference sites is described in the report, Biological Assessment of Iowa's Wadeable Streams (PDF) (270 pp, 4 MB).

The program also utilizes qualitative reference site selection criteria for 11 core factors described in Appendix 2 of the report, Identification and Quantification of Reference Conditions Associated with Lotic Ecosystems of the Central Plains and Surrounding Regions: A summary of approaches and factors and regional approach (PDF) (34 pp, 277 K).

Not applicable.

Stressor identification/causal analysis approach:
Iowa DNR has used Stressor Identification primarily to determine the causes of biological impairment including any pollutant for which a Total Maximum Daily Load (TMDL) is required. The Iowa DNR has a protocol for stressor identification and causal analysis, which closely follows the steps outlined in “Stressor Identification Guidance Document” (USEPA 2000).

Technical reference material: 
Water Improvement Plans; an example of a Stressor Identification report can be found in the document library under Final Water Quality Improvement Plans

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