Delaware’s Inland Bays Watershed- Courtesy University of Delaware

Watersheds of the Inland Bays

Assawoman | Buntings Branch | Indian River | Indian River Bay | Iron Branch | Lewes-Rehoboth Canal | Little Assawoman | Rehoboth Bay


The Inland Bay waters are highly enriched with the nutrients nitrogen and phosphorus, the contaminants having the greatest impact on the surface and groundwater of the Inland Bays. While nitrogen and phosphorus are essential for plant and animal growth, when excess amounts enter the bays, water quality can deteriorate as aquatic plant growth accelerates and the level of oxygen is reduced, leading to eutrophication.

Existing contamination may be the result of either pastor present human activities. Past practices, such as landfill operations (now closed) and Superfund sites, may still be contaminant sources. Contamination from current activities may occur routinely, as in a permitted discharge of a municipal wastewater treatment plant; or may occur as a result of a spill or leak, as in ground-water contamination from a leaking underground storage tank. Contamination may be transported or exchanged between various media, such as a contaminant that was land applied that is subsequently transported in ground or surface water.

water shed

Nitrogen and phosphorus originating from agricultural activities have been identified as key factors in non-point source pollution in the Inland Bays/Atlantic Ocean Basin. There are approximately 72,000 acres of agricultural land in the Basin, representing more than 40 percent of the total land area. The majority of croplands are devoted to growing corn, soybeans, and sorghum, which go to feed the Basin’s thriving poultry industry. Agricultural lands are highly susceptible to nutrient loss. Factors such as soil type, depth-to-ground water, topography, ditches and drainage ways, and precipitation all affect nutrient transport in the Basin.

Water-quality samples collected from several agricultural drainage waters within the Basin show elevated levels of both nitrogen and phosphorus in the waters, at levels that exceed water-quality standards for streams in the Basin. Average nitrate concentrations in the waters from two sites averaged 5.8 and 4.6 mg/l. Ammonia nitrogen was also found in the waters ranging from 1.0 to 9.1 mg/l at one site and 0.18 to 6.8 mg/l at another. These values exceed the 0.14 mg/l water quality standard for nitrogen in the Basin. Total phosphorus levels in the waters were also consistently higher than the 0.01 mg/l phosphorus water-quality standard for the Inland Bays. Values of total phosphorus ranged from below detection levels to 0.34 mg/l at one site and 1.7 mg/l at another.

Size: 410 square miles

Population: 112280

Source: U.S. Census

Land Use:

Source: NOAA Coastal Services Center (CSC), Coastal Change Analysis Program (C-CAP) Land Cover data based on analysis of Landsat 30m resolution imagery.

States: DE

Counties: DE: Sussex

U of D University of Delaware Citizen Monitoring Program

Since 1991, our dedicated corps of Citizen Monitoring volunteers have been taking water samples on a regular basis throughout Delaware’s coastal watershed to measure a broad range of important water quality characteristics. The data they gather…(read more…)