Lake Manassas is a 770-acre (310 ha) reservoir located in Prince William County, Virginia, to the southwest of Gainesville.

[3] The reservoir was created in the late 1960s to provide drinking water for area residents and became operational in 1970.

Beginning in the 1980s, and continuing until 1995, public access to the lake was possible via a private marina.

[2] Periodic attempts have been made by the city, county, and various others to reopen the lake for public use;[4][6] however, as of April 2012, none have been successful.

In June 2010, officials from the Virginia Department of Game and Inland Fisheries and George Mason University's Freedom Aquatic & Fitness Center presented a plan to use the donated land as a marina, however the City Council never acted to accept or reject the proposal, citing continued concerns over operating costs and how the marina would be managed to ensure the protection of the drinking water supply.