DEEP Fish Community Data - Inland Waters

The DEEP Fish Community Viewer showcases fish and macroinvertebrate data for Connecticut's inland waters. Information is provided below about what is included and how this data is collected. Disclaimer: Please be aware of the sample year. Biological condition can change over time and some of the data may or may not be representeative of current conditions.

Fish Community:

Fish community data are routinely collected by CT DEEP in rivers/streams and lakes/ponds for a variety of reasons. Data presented here were collected using electrofishing equipment, an efficient non-lethal method to collect fish.  Immediately after being collected, each fish is identified, measured and released.  In lake and ponds, a scale sample may be collected to help determine age and growth rate.

Appropriate Use: Data represent the number of each species counted during whole community census or “all species” samples. Please note, these numbers may not be directly comparable from one sample or location to another as sampling effort may vary. DEEP fisheries has other fish and fisheries related data that are single species specific, gamefish specific, or collected with gear other than electrofishing equipment.  These data can be made available upon request. Questions about the data should be directed to or 860-424-FISH.

photo: CT DEEP


Macroinvertebrates include aquatic insects, worms, crustaceans and other animals.  Macroinvertebrates are one of the most commonly used communities to assess water quality. Since the 1970’s the water quality monitoring program within the Bureau of Water Protection and Land Reuse has been collecting and evaluating river/stream macroinvertebrate data. These samples are usually identified to the genus or species, however, for this application data are presented as the number of different genera within a family.

Appropriate Use: Data represent the number of genera identified in the sample that are within the family.  These samples represent the occurrence of a family (and different genera) at each location on the referenced year.  In some cases, this list may be a composite of several different types of sample collection methodologies (for example a kick net and artificial substrate like a rock basket).

You can be involved! The DEEP encourages citizens to collaborate with DEEP to help collect the “most wanted” macroinvertebrates from wadeable rivers and streams.  Get all of the details on the Riffle Bioassessment by Volunteers web page.

photo: CT DEEP


Fish, macroinvertebrate, water quality and water quantity data are evaluated against state water quality standards every two (2) years as required under the Federal Clean Water Act.  All comprehensive biological assessments are published in the integrated water quality report

One tool currently in development for this type of assessment is the  Biological Condition Gradient (BCG).  The  BCG is a ranking system from 1 (natural) to 6 (dysfunctional) developed by U.S. Environmental Protection Agency (EPA) to provide a common language to describe a particular community of living organisms. To learn more about how this conceptual model in used in Connecticut, visit the CT DEEP website.  

In general, BCG values of one (1), two (2), or three (3) can be intrepreted as “high” and may be considered to support Connecticut’s aquatic life standard.  A value of four (4 )is considered on the border (moderate), which may or may not support the standard, and a value of five (5) or six (6) is considered to not support the aquatic life standard (low).  As fish and macroinvertebrates have different susceptibility to environmental stressors, fish and macroinvertebrates BCG scores can be different from the same location in the same year. 


Point of Contact:

Questions about the data should be directed to or 860-424-FISH.