Public Works and Environmental Services

CONTACT INFORMATION: Our administrative offices are open 8 a.m. – 4:30 p.m., Mon - Fri
703-324-5500 TTY 711
12000 Government Center Parkway
Suite 449, Fairfax, Va 22035
Joni Calmbacher
Director, Stormwater Planning

Stream Quality Assessment Program

A stream is a combination of all of its physical, chemical and biological characteristics. Human activities shape and alter many of these characteristics. The health of our rivers and streams is closely linked to their surrounding watersheds. Ecologists measure the extent to which human activities affect watershed health by gathering and recording information on physical conditions, water quality and living communities in streams and in the surrounding environment. 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 streams. The program maintains a substantial database, which over time will be used to determine the overall rate of change or trends in the conditions of our waterways.

Freshwater ecologists monitor Fairfax County’s streams and lakes to assess water and habitat quality and gauge the overall health of waterways. The long-term stream monitoring program meets the requirements of state and federal regulations and supports the Board of Supervisors' environmental improvement program.

Stream Conditions

Fairfax County collects biological data at 40 randomly selected locations each year. The Stream Quality Index (SQI) is based on annual data collected on benthic macroinvertebrates (animals without a backbone that live on the bottom of a stream and are visible to the naked eye). The SQI uses benthic macroinvertebrates because they are good indicators of water quality.

Each of the 40 locations receives a score (excellent, good, fair, poor, or very poor) based on the benthic macroinvertebrates found in that stream. The higher SQIs indicate better stream quality. In many years, greater than 75 percent of Fairfax County's streams are in fair, poor, or very poor biological condition. This indicates that most of our streams are impaired and lack biological diversity. Annual results can be found in the table below.


Monitoring Methods

Countywide monitoring is conducted annually using a probabilistic design approach. Using this approach, statistically valid inferences may be made about the condition of the county's streams. Each year, all potential sampling sites are stratified by stream order and 40 sampling locations are selected randomly. These 40 locations are then evaluated for bacteria levels, benthic macroinvertebrates, fish community and physical habitat during that year. Water quality parameters (such as water temperature, dissolved oxygen, specific conductance, pH and levels of nitrogen and phosphorus) are also collected. The results of the yearly monitoring events are compiled into annual reports  and are used to support the county's Environmental Quality Advisory Council's Annual Report on the Environment. The protocols for macroinvertebrate and fish monitoring and habitat assessment are based on the EPA's Rapid Bioassessment Protocol for Use in Wadeable Streams and Rivers. The modified protocols can be found in the Standard Operating Procedures Manual for the Fairfax County Biological Stream Monitoring Program.

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