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TextStream Quality Assessment Program
The long-term stream monitoring program meets the requirements of state and federal regulations and supports the Board of Supervisors' environmental improvement program by providing an ongoing evaluation of the physical, chemical and biological conditions for Fairfax County's streams. Stream and watershed health is evaluated using a variety of indicators such as water quality parameters, bacteria levels, resident invertebrate and fish communities and habitat conditions.
The study evaluates countywide stream health conditions annually through a randomized site selection process. The program is developing a substantial database, which over time will be used to determine the overall rate of change or trends in the conditions of our waterways.
Stream Conditions
Based on biological data collected at 40 randomly selected locations
(see map of
monitoring site locations) throughout Fairfax County in
2009, approximately 88 percent of Fairfax County's streams are in
fair to very poor condition. This indicates a notable decrease in
biological diversity and that many of our streams are significantly
impaired. More information about the 2009 biological monitoring
results can be found in the 2009
Fairfax County Stormwater Status Report.
The Stream Quality Index is computed based on the benthic macroinvertebrate data that are collected by the county. This index is reported annually to evaluate trends in the overall health of streams countywide.
The index values for the 2009 stratified random sampling data suggest a small decline in overall stream quality from the previous year. However, it is difficult to make any broad statements about trends in the overall health of streams countywide based on data from only a few years of sampling. As more data is collected, the trends in streams conditions countywide will be more valid and more apparent.
Monitoring Methods
The original monitoring design, which used targeted sites, was updated in 2004 to a probabilistic monitoring approach. This methodology, which is now widely used by other monitoring agencies (including the commonwealth of Virginia), evaluates sites which are randomly selected within Fairfax County each year. Every year, 40 stream locations are monitored for several parameters including: bacteria, benthic macroinvertebrates, fish and physical habitat. Water quality parameters, such as water temperature, dissolved oxygen, specific conductance, pH and nutrients such as nitrogen and phosphorus are also collected. The results of the monitoring events are compiled into annual reports and are also used to support the county's Environmental Quality Advisory Council's Annual Report on the Environment. More information on specific monitoring methods can be found by selecting the below monitoring category.
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| Bacteria and Water Chemistry | Benthic Macroinvertebrates | Fish Community | Habitat Quality |
For more information on the county's Stream Quality Assessment Program, please e-mail the Stormwater Planning Division or call 703-324-5500, TTY 711.
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