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

State Program Contact

Delaware Department of Natural Resources and Environmental Control Exit

Water Quality Standards

WQS Information
The link to Delaware's WQS that are in effect for Clean Water Act purposes is provided. These are the WQS approved by EPA.
The state of Delaware 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
All waters have a single aquatic life use. A (very) small subset also has “Cold Water Fish (put and take)” use to support annual stocked fish program. 

Biological Criteria
_____ Narrative
_____ Numeric
__X__ No criteria

Antidegradation Policy
Section 5.0 of our WQS has narrative regarding Antidegradation (PDF) (35 pp, 420 K, About PDF). No specific biological criteria are in our WQS.

Biological Assessment

What biological assemblages are used in the bioassessment program?
Benthic macroinvertebrates only.

Are bioassessments used to support 303(d) listings?
Yes and No. Listing methodology: In the past, the Department made listing decisions to list for “Biology”, “Habitat” or “Biology and Habitat” based on comparisons of stream conditions to reference streams. We are working our way through the resultant 303(d) listings at this time. 

How are assemblages used to make impairment decisions?
Not actively making impairment decisions at this time as we work through the past listing decisions.

Other uses of biocriteria or bioassessment within the water quality program:
TMDL development and assessment

Technical Support Information and Documents:

Reference condition:
DE has no ‘reference’ sites. IBIs are based on the 5th/95th percentile of all sites sampled at time of creation. We use ‘control’ sites that represent the best known sites in the state, based on previous sampling, to evaluate changes over the years.

Not applicable.

Stressor identification/causal analysis approach:
Under development.

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