Benthic Monitoring

Benthic Monitoring is the study of the critters that live on the bottom of the stream. Their health determines the health of the stream. Their numbers and diversity also help determine the degree of health if a stream.

Benthic Monitoring is a method of monitoring a stream bed for the bottom dwellers of the stream. A healthy stream will have a large variety of macroinvertabrates which are the "critters" that live on the bottom of the stream amongst the rocks and mud. They are an extremely important part of the river's ecosystem. These "critters" are insects, worms and clams. Over time,crayfish monitoring the amount of these organisms in a stream will give an idea of how healthy the stream is because these little guys can't survive a lot of pollution and chemicals.

When a stream is monitored, the macroinvertabrates are collected and counted, and then a score is given according to the number found. The score is then recorded with a state agency to help monitor the health of the stream.
View more critters like this crayfish at our Benthic Critters page.

Why Do Benthic Monitoring?

  • Stream Impairment & TMDLs

A Total Maximum Daily Load (TMDL) is a regulatory term in the U.S. Clean Water Act (CWA), describing a value of the maximum amount of a pollutant that a body of water can receive while still meeting water quality standards. Alternatively, TMDL is an allocation of that water pollutant deemed acceptable to the subject receiving waters. TMDLs have been used extensively by the United States Environmental Protection Agency (EPA) and state environmental agencies in implementing the CWA by establishing maximum pollution limits for industrial wastewater dischargers. EPA published regulations in 1992 establishing TMDL procedures. Application of TMDL has broadened significantly in the last decade to include many watershed-scale efforts. This process incorporates both point source and nonpoint source pollutants within a watershed.

  • Erosion and Sediment

Construction sites that do not control the disturbed soils they may be removing for a new building eventually end up in the streams as sediment. The sediment builds up in the stream and puts stress on the survival of the insects. Controls are monitored so that the least amount of sediment as possible is added to the streams.  Virginia's DCR has regulations and standards that construction sites have to follow and to minimize the erosion impact on our streams.

  • Stormwater Runoff

When large rains wash mud, oils, pollution in general from our streets and pesticides from our fields it usually goes directly into our streams. Most communities do not send the runoff through a wastewater facility where it could be cleaned before entering the streams so this dirty water is contributing to the pollution and sediments in the streams adding to the impairments of many of VA's streams. Solutions to runoff include: rain gardens, riparian buffers, and better drainage systems, street sweeping, stormwater detention ponds. These solutions effectively reduce the release of pollutants into our streams.


To learn more about Benthic Monitoring and Benthic critters and who they really are check out these sites and documents.

For a quick overview of benthic monitoring, this site is good, and if you are a trout fisherman and are curious about the importance of these insects to the fish is a great resource for more information.  He has given us permission to reference his site and to use some of the bug photos.

Friends of the North Fork has a Benthic Program that needs YOU!

If you are interested in our Benthic Monitoring Program, call for details at 540-459-8550 or email us


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PO Box 746, Woodstock, VA, 22664     540-459-8550

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