An Investigation of the Limnological Dynamics of Lake Manassas

Lake Manassas, located in the Occoquan Watershed in Virginia is a man-made impoundment of the Broad Run river. This lake surface area is approximately 697 acres, and it drains approximately 46,500 acres. Currently, the reservoir supplies drinking water to the City of Manassas and some areas of Western Prince William County, but if necessary, can help supply drinking water to 750,000 people in the Northern Virginia area.

Since 1984, the Occoquan Watershed Monitoring Laboratory has been sampling seven streams and eight lake stations as part of a program funded by of the City of Manassas. Lake Manassas is an important drinking water resource for the City and the surrounding areas and is used for recreational purposes as well. It is extremely important to continuously monitor the lake closely so that any6 undesirable trends in water quality may be detected and addressed. Currently surrounding the lake are two golf courses, with two more golf courses planned for the future, as well as homes, and recreational areas.

Overall, Lake Manassas is still considered to be eutrophic, which is the same conclusion reached in previous reports. The main nutrient source is Broad Run, but there are other smaller sources as well that are of concern. South Run has decreased nutrient loadings since the last report in 1996. Another conclusion is that the lake is Phosphorus-limited, but at times, the lake comes close to being nitrogen-limited.