Occoquan Watershed Program

Occoquan Locational Map


The Occoquan Watershed covers about 590 square miles and includes the Occoquan Reservoir, which serves as the boundary between Fairfax and Prince William counties. The reservoir is one of two major water sources for the Fairfax County Water Authority, which supplies water to over one million people in Northern Virginia.
Occoquan Subbasins


The purpose of NVRC's Occoquan Basin Nonpoint Pollution Management Program is to help localities maintain acceptable water quality in the reservoir through control of nonpoint source pollutant loadings. NVRC maintains the Occoquan Basin Computer Model, which during the early 1980s served as the basis for down zoning the Fairfax County portion of the watershed to protect drinking water from pollution caused by urban development.

Land Use Updates

Every five years, NVRC performs an assessment of land use changes in the watershed to update the model. This helps localities determine whether additional land management efforts are necessary. Over time, more accurate data and updated technology have become available and NVRC’s land use tracking methodology has changed along with it. 

For the 2015 Land Use Update, NVRC developed a new land use tracking methodology that focuses on impervious and pervious surface area. The detailed methodology for this update is discussed in the White Paper: Updating the 2015 Land Use for the Occoquan Watershed. NVRC will continue to update the land use for the Occoquan Watershed every five years, now using the updated methodology discussed in the contents of this paper.