Fish of Montgomery County
Montgomery County is home to more than 60 species of freshwater fish, representing nearly every family of freshwater fish known in Maryland. This includes trout, catfishes, sunfishes and bass, minnows, suckers, sculpins, darters and perch, killifishes, lampreys, American eel, Eastern mudminnow, and Eastern mosquitofish.
Fish are important to Montgomery County stream ecosystems. They are part of our natural history, provide food, recreation and have intrinsic and economic value. Fish also play a vital ecological role in the overall food web. County biologists study fish communities to provide insight on the health and condition of County streams.
Want to help protect our fish and learn more?
Montgomery County divides fish into three groups based on their ability to survive in polluted waters. Sensitive fish are only able to survive in the county's highest quality streams. Moderately tolerant fish can survive and sometimes thrive in areas that receive minor pollution. Tolerant fish live in most streams in the county, but they are the only fish that can survive in heavily polluted waters.
Each fish has unique requirements for where they live. Check out what species live around you with Maryland Fish Distributions Maps!
Highly Sensitive Fish
Pollution Tolerant Fish
Why are they Important?
Fish are indicators of water quality:
Fish provide scientists insight into past stream conditions. When a stream is stressed, fish communities respond over time. Streams stressed by excessive sediment have less desirable habitat and lose sensitive fish species like Blueridge Sculpin.
If the water is polluted, then fish may develop lesions or may have physical deformities.
Monitoring and Data
Stream biologists study fish species and any changes in their population size over time, because fish serve as biological indicators of water quality.
The Department of Environmental Protection identifies and studies fish in County streams by conducting field testing using electrofishing. Visit our electrofishing page for more information on the process.
What Data Does DEP Collect?
Fish IBI Metrics
Once numbers of individuals are summed for each species present at a stream site, a fish Index of Biotic Integrity (IBI) is calculated based on multiple metrics. The IBI is used to rank the stream in relation to reference stream conditions. To use biological data properly, water resource analysts generally compare the fish data (actually not the raw data but a multi-metric index based on the data) from the stream sites under study, to indices from stream sites in ideal or nearly ideal condition (often called a reference condition). Stream sites are then ranked against the reference condition. This helps DEP set priorities for watershed restoration and improvement.
The fish IBI is averaged with the benthic macroinvertebrate IBI to determine overall stream conditions.
Fish IBI metrics are listed below. A technical, peer-reviewed methodology is used to take raw data and develop them into an acceptable Stream Rating score.
Montgomery County has tabular raw fish data and fish narrative summaries from 1994-present for most monitoring sites around the County. Also available are GIS coverages (or maps) showing fish conditions. Maps can be developed to order depending on the request. Submit a request for either raw data or data in maps.
The following tables provide an explanation of the datafields found in our raw tabular data:
To request data, send an email to email@example.com with the following information:
Interested in other DEP monitoring data? Request fish, benthic macroinvertebrates, herptofauna and stream habitat data too.