Headwaters to Baywaters

The Occoquan Watershed drains 590 square miles, beginning in the forested Bull Run Mountains to the northwest as three small spring-fed streams that are joined by others to form Bull Run. About 10 miles downstream from here, Bull Run meets the Occoquan River, which fills the Occoquan Reservoir, a source of drinking water for over 1 million Northern Virginians. Below the dam, some fresh water continues onward, mixing with the salty tidal water of the Potomac River before flowing to the Chesapeake Bay. While mountains, valleys, and tidal plains shape Bull Run's journey to the bay, forests define the watershed's health by filtering pollutants and holding soil in place, and keeping or planting trees, shrubs, and groundcover helps keep water healthy. Harry Ardell Allard, an internationally known botanist who loved the Bull Run Mountains, discovered how the duration of light and darkness affects the flowering and germination of plants, and in the 1930s and 1940s he made 55 trips a year to this region, collecting nearly 15,000 plant specimens and describing their habitat. Efforts today to protect and restore the watershed still rely on images from Allard's field notes.

Bull Run, Virginia · United States