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About the Bays

Delaware’s Inland Bays consist of three interconnected bodies of water in southeastern Sussex County: Indian River Bay, Little Assawoman Bay, and Rehoboth Bay.

The Inland Bays are shallow, with an average depth ranging from 3 to 8 feet. Because the bays are so shallow, and because they are poorly flushed by tidal movement, they are especially sensitive to environmental changes. Increases in pollutants, changes in salinity, and fluctuations in water temperature, for example, can have dramatic effects on water quality and on the plants, fish, shellfish, and microscopic creatures that live in the bays.


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The Inland Bays Watershed

The bays and their tributaries cover about 32 square miles and drain a land masscalled a “watershed”of about 320 square miles.  

The watershed itself reaches to the north to the southern edge of the Delaware Bay in Lewes. From there, it extends south through Rehoboth Beach, Dewey Beach, Bethany Beach, and South Bethany to its southern border in Fenwick Island at the Maryland state line.

Heading west, the Inland Bays watershed weaves through the eastern portion of Sussex County, enveloping the towns nearest Route 113 including Selbyville, Frankford, Dagsboro, Millsboro, and Georgetown, and ending just before reaching Route 404.


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Issues Affecting the Bays

Two major areas of concern have been identified as critical issues for Delaware’s Inland Bays: eutrophication (rapid plant growth due to excessive nutrients) and habitat loss.

Due to urbanization, agricultural activities, and low flushing rates, the Bays have become highly enriched with nitrogen and phosphorus. While these nutrients are essential for plant and animal growth, water quality can deteriorate when nutrients are present in excessive amounts. When that happens, algal growth accelerates and oxygen levels drop, making it difficult or impossible for organisms like fish or crabs to survive.

In December 1998, the Delaware Department of Natural Resources and Environmental Control set Total Maximum Daily Loads (TMDLs) for nitrogen and phosphorus for the Indian River and Rehoboth Bays. A TMDL was created for Little Assawoman Bay in December 2004.

TMDLs, as defined by the U.S. Environmental Protection Agency, calculate the maximum amount of a pollutant allowed to enter a waterbody so that the waterbody can meet water quality standards. A TMDL sets a “pollutant reduction target” and “load reductions” necessary to target the source(s) of the pollutant so that impaired waterways can once again be fishable or swimmable.

Water quality goals created in those TMDLs call for eliminating all “point sources” of pollution directly entering these water bodies. A “point source” could be something like an outfall pipe that sends treated stormwater or wastewater into the Bays and/or their tributaries. “Nonpoint sources” of pollution can include runoff from lawns or impervious surfaces, which does not come from an easily identified pipe or other source.

The TMDLs also require a 40% reduction in nonpoint phosphorus pollution in the Indian River, Rehoboth, and Little Assawoman Bays and a 65% reduction in the upper Indian River watershed; a 40% reduction of nonpoint nitrogen loading in the Indian River Bay, Rehoboth Bay, and Little Assawoman Bay and an 85% reduction in the upper Indian River watershed. 

The concerns related to nutrient over-enrichment in the Bays means there needs to be a reduction in nutrients coming from a variety of point and nonpoint sources in the watershed. 

In addition to these problems, the loss of valuable aquatic, upland, and wetland habitats are also stressors on water quality in the Inland Bays.


Further Reading…

These books have been hand-selected to help you learn more about our Inland Bays watershed. Anything marked with an asterisk is *Great to read to children, yet informative for adults.

  • Between the Ocean and Bay: A Natural History of Delmarva, Jane Scott
  • A Place Between the Tides: A Naturalist’s Reflections on the Salt Marsh, Harry Thurston
  • Between Ocean and Bay: A Celebration of the Eastern Shore, Jim Clark
  • Teaching the Trees: Lessons from the Forest, Joan Maloof
  • Delaware Trees, William S. Taber
  • Common Plants of the Mid-Atlantic Coast:  A Field Guide, Gene M. Silberhorn 
  • Horseshoe Crab Biography of a Survivor, Anthony D. Fredericks
  • *Horseshoe Crabs and Shorebirds:  The Story of a Foodweb, Victoria Cresson and Annie Cannon
  • *Crab Moon, Ruth Horwitz
  • Birds of Delaware (Pitt Series in Nature and Natural History), Gene Hess and Richard West
  • *Red Knot: A Shorebird’s Incredible Journey, Nancy Carol Wilis
  • The Flight of the Red Knot: A Natural History Account of a Small Bird’s Annual Migration from the Artic Circle to the Tip of South America and Back, Brian Harrington
  • The Narrow Edge: A Tiny Bird, an Ancient Crab, and an Epic Journey, Deborah Cramer
  • Salt Marshes: A Natural and Unnatural History, Judith S. Weis and Carol A. Butler
  • *A Journey into an Estuary, Rebecca L. Johnson