The Occoquan Watershed covers 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.

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.

Every five years, NVRC performs an assessment of changes in land uses in the watershed to update the model and to help localities determine whether additional land management efforts need to be undertaken.