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 This website is no longer updated and links to external websites and some internal pages may not work.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 Maryland: Streams and Wadeable Rivers

State Program Contact

Maryland Department of the Environment - Biological Stream Survey Exit

Water Quality Standards

WQS Information
The link to Maryland's WQS that are in effect for Clean Water Act purposes is provided. These are the WQS approved by EPA.
The state of Maryland 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
Maryland’s ALU are mainly distinguished by aquatic life types, i.e, warmwater vs. coldwater. However, we also have a classification for tidally-influenced waters, and waters used for put and take trout fishing (refer to Designated Uses for more information).

  • Use Class I – warmwater aquatic life
  • Use Class II – tidal aquatic life
  • Use Class III – coldwater aquatic life
  • Use Class IV – Put and Take trout fishing areas

Any one of these Use Classes can be given the “-P” suffix which indicates the water body as a public drinking water source or that is upstream of a public drinking water source.

Biological Criteria
__X__ Narrative, with quantitative implementation procedures or translators
_____ Numeric
_____ No criteria

Maryland has narrative biocriteria specified in Code of Maryland Regulations (COMAR) These criteria are based on quantitative biological indices that are assessed according to Maryland's publicly reviewed Biological Assessment Methodology for Nontidal Wadeable Streams.

Code of Maryland Regulations (COMAR) Biological Water Quality Criteria
A. Quantitative assessments of biological communities in streams (biological criteria) may be used separately or in conjunction with the chemical and physical criteria promulgated in this chapter to assess whether water quality is consistent with the purposes and uses in Regulations .01 and .02 of this chapter.
B. The results of the quantitative assessments of biological communities shall be used for purposes of water quality assessment, including, but not limited to, those assessments required by §§303(d) and 305(b) of the federal Clean Water Act (33 U.S.C. §§1313(d) and 1315(b)).
C. These assessments shall use documented methods that have been subject to technical review, produce consistent and repeatable results, and are objectively interpretable.
D. In using biological criteria to determine whether aquatic life uses are being met, the Department shall allow for the uncertainty and natural variability in environmental monitoring results by using established quantitative and statistical methodologies to establish the appropriate level of uncertainty for these determinations.
E. The Department shall determine whether the application and interpretation of the assessment method are appropriate. In those instances where the Department determines the assessment method is not appropriate, it will provide its justification for that determination.

Antidegradation Policy
COMAR D.(3)(b) Antidegradation Policy Implementation Procedures
Biological assessment data indicate water quality is within 20 percent of the maximum attainable value of the index of biological integrity.

Biological Assessment

What biological assemblages are used in the bioassessment program?
Benthic macroinvertebrates, fish, amphibians, mussels, and crawfish

Are bioassessments used to support 303(d) listings? 
Yes. Listing methodology: Biological Assessment Methodology for Non-Tidal Wadeable Streams (PDF) (29 pp, 645 K)
MDE Requirements for Use of In-Situ Biological Stream Data (PDF) (15 pp, 220 K)

How are assemblages used to make impairment decisions?
Only fish and benthos are used for 303(d) assessment. Fish and benthos are applied independently to make impairment determinations. If one fails to meet the conditions of the assessment methodology, then the entire sample site is considered to be impaired. They are weighted evenly.

Other uses of biocriteria or bioassessment within the water quality program:
Refining ALU/existing use determinations, determining the applicable water quality criteria, TMDL development and assessment, antidegradation, non-point source assessments, BMP evaluation, 305(b) surface water condition assessments, and restoration goals.

Technical Support Information and Documents:

Reference condition:
The IBIs used in biocriteria assessment are based off of the aquatic assemblages found at reference sites defined by the following abiotic variables. Please note that there is a lot more detail to the reference condition development than these features all of which are detailed in the document located at the link provided below.

  • pH ≥ 6 or blackwater stream (pH < 6 and DOC ≥ 8 mg/l)
  • ANC ≥ 50 Feq/l
  • DO ≥ 4 ppm
  • nitrate ≤ 300 Feq/l (4.2 mg/l)
  • remoteness rating: optimal or suboptimal
  • aesthetics rating: optimal or suboptimal
  • instream habitat rating: optimal or suboptimal
  • no channelization
  • no point source discharges

Technical reference material:
Maryland Biological Stream Survey Round Four Sampling Manual (PDF)(86 pp, 2 MB)

Development of biocriteria involves the collection and interpretation of biological data –e.g. benthic macroinvertebrates, fish, and periphyton. During this process entities typically use biological metrics (usually aggregated into a multimetric index) and/or multivariate analysis to assess whether a waterbody is meeting its designated aquatic life use(s). The reference materials included below include standard operation procedures used in data collection, compilation, technical approaches used to develop biocriteria as well as its implementation procedures.

Technical reference material:
Maryland Biological Stream Survey 2000-2004 (PDF) (69 pp, 2 MB)
Maryland Biological Stream Survey Online Publications

Stressor identification/causal analysis approach:
Stressor identification and casual analysis are linked by concomitant monitoring for biota and stressors.

Technical reference material:
Biological Stressor Identification Studies

Top of Page