Stream Monitoring in Fairfax County

Stream monitoring workshops are only announced through the Watershed Calendar. You can register for this email listserve here or by emailing NVSWCD.

NVSWCD assesses the ecological condition of several Fairfax County streams based on the presence and abundance of benthic macroinvertebrates (aquatic insects).

NVSWCD’s volunteer stream monitoring program began in 1997 and has grown to be one of the largest and longest-running volunteer stream monitoring programs in Virginia. Our program began through the dedication of local monitors and continues as a result of our enthusiastic and committed volunteers. They trudge through tall grass, sink in muck, and break through ice to monitor their streams.

The exact number of monitoring sites changes due to the availability of volunteer monitors and changes in stream morphology and water levels. NVSWCD manages data for approximately 20-30 stream monitoring sites, most of which are monitored exclusively by local volunteers. Locally, our data is used in the Fairfax County Stream Protection Strategy Program, and our volunteers are the first to notify us if their stream becomes impaired. 

Aquatic Benthic Macroinvertebrates and Water Quality

Every year hundreds of streams in the United States are contaminated by pollutants that degrade their overall health. What most people do not realize is that a large portion of this stream degradation is attributed to us. After a rainfall event, paved areas and rooftops create large volumes of surface runoff that pick up contaminants on our roads and lawns (such as oil and fertilizer) before flowing into storm drains which channel the polluted runoff directly to our streams. Fairfax County has 30 major stream watersheds, all of which feed into the Potomac River and Chesapeake Bay. Both the increased runoff volume as well as the contaminants can have very adverse effects on our aquatic ecosystems, and in particular, on our populations of benthic macroinvertebrates.

What are macroinvertebrates and why are they so important to the health of our streams? Benthic macroinvertebrates are small but visible aquatic animals without a backbone that live at the bottom of streams for at least some portion of their lives. They can be found under logs, sediment, rocks and aquatic vegetation.

Some common examples of these animals are: crayfish, clams, snails, aquatic worms, and a variety of aquatic insect larvae, such as stoneflies, caddisflies, mayflies, dragonflies and damselflies. In addition to being an integral part of the aquatic food chain, they are also used to draw conclusions about the overall health of our streams.

How are macroinvertebrates used to measure stream health? Macroinvertebrates, unlike fish and other aquatic vertebrates, are less mobile and therefore less able to escape the effects of habitat degradation. Their abundance and species diversity can be used to measure stream health. They live year-round in the stream which helps in continual water quality studies. Each species responds to contaminants and stress differently. This allows for better determination of problems that are plaguing our streams. In addition, certain macroinvertebrates such as stoneflies, caddisflies and mayflies can also act as early warning indicators of changes to the stream, in particular, through contamination from point and nonpoint sources. These specific macroinvertebrates are very sensitive to stream impairment and need good water quality, cool temperatures, and a high concentration of dissolved oxygen to survive.

Virginia Save Our Streams and Macroinvertebrates

Often, when we think about determining water quality, we imagine chemical tests such as pH, dissolved oxygen or nitrate testing. Although these give us a numerical value as to the quality of our water, the numbers are subject to high variability within the stream. A less expensive, more efficient method involves using biological monitoring to evaluate the abundance and diversity of benthic macroinvertebrates found in the stream to assess habitat quality.

Macroinvertebrates are collected using a net positioned on the stream bed as rocks and sediment are overturned. After each catch, the macroinvertebrates are identified, sorted by species and recorded on a data sheet. At the end of the stream monitoring session, some simple calculations are made and an ecological score is determined. A typical stream monitoring site should be sampled at least two times a year during each season to get an accurate assessment of the changing quality of the stream.

NVSWCD follows the stream monitoring protocol outlined by the Izaak Walton League of America’s Virginia Save Our Streams (VASOS) Program. The VASOS Rocky Bottom Protocol outlines how often streams can be sampled, the proper equipment and techniques used to sample them, and how to calculate a stream score using the number and biodiversity of macroinvertebrate species sampled. You can learn more about VASOS by visiting their website. A healthy stream has a large number and wide variety of macroinvertebrates. There are many resources for learning more about macroinvertebrates, including identification resources from VASOS and the interactive online Atlas of Common Freshwater Invertebrates of North America.

NVSWCD stream monitoring sites are sampled 2-4 times yearly and the data is reported to VASOS. VASOS performs quality control on the data and forwards it to the Virginia Department of Environmental Quality where it is used to make state-wide stream management decisions. You can also see all the data from NVSWCD workshops sites and certified monitor sites on this map from the Clean Water Hub. Data is made available to the public with a free account; username and password are required to create the account. 

Become a Volunteer Stream Monitor!

You can gain stream monitoring experience and service hours by attending a stream monitoring workshop. NVSWCD Stream Monitoring workshops are open to the public and held March-November yearly, with more workshops occurring during the spring and fall monitoring seasons. Workshops are held at NVSWCD stream sites throughout the county and last approximately 3 hours. Volunteers learn about watersheds and water quality, collect macroinvertebrates, sort and identify the macroinvertebrates caught, and calculate a stream health score.

• Why monitor streams as a volunteer?
• See the Stream Monitoring Handbook for program information, safety guidelines and more.

Want to join NVSWCD at a stream monitoring workshop? 

Stream monitoring workshops offered by NVSWCD and other local stream monitoring groups are announced in NVSWCD’s monthly email newsletter, the Watershed Calendar. You can register for the email listserve here or by emailing NVSWCD.

Interested in becoming a certified stream monitor?

VASOS and the Izaak Walton League of America offer a stream monitoring certification for interested volunteers. It is recommended that you attend at least 2 workshops with NVSWCD or another stream monitoring group before pursuing your certification. Certification consists of online training and a test on macroinvertebrate identification as well as an in-person practical field exam in a nearby stream on VASOS monitoring protocols. After you become certified, you can join one of NVSWCD’s volunteer-led Stream Teams, start a Stream Team at a new monitoring site, or continue to assist in our stream monitoring workshops. Stream monitoring certification lasts for two years, or as long as you continue to submit stream monitoring data to VASOS. 

You can learn more about the VASOS/IWLA stream monitoring certification and begin your journey here. 

Meet Your Streams! 

NVSWCD monitors several streams throughout Fairfax County during our scheduled stream monitoring workshops, which engage volunteers from the public in collecting data from these sites. Each location has a scheduledd monitoring session at least twice per year, in spring and fall, and often more frequently if weather and scheduling allow. All of the data collected at NVSWCD stream monitoring sites is submitted to the VASOS Data Portal as well as the Clean Water Hub, where you can see all the data from NVSWCD workshops sites and certified monitor sites. 

Fairfax County is home to 30 major watersheds and many smaller subwatersheds. Visit the Watersheds webpage to learn more about watersheds and streams in Fairfax County.

Want to join NVSWCD at a stream monitoring workshop?

Stream monitoring workshops are only announced through the Watershed Calendar. You can register for this email listserve here or by emailing NVSWCD.