Region Three is located on the east coast in the Mid-Atlantic area. The region is bounded by North Carolina, Ohio, New Jersey and New York. The region is comprised of the following states: Delaware, Washington DC, Maryland, Pennsylvania, Virginia and West Virginia.

Region 3 is home to a number of water bodies, but the Chesapeake Bay and its tributaries are the largest and most important in the area. The Chesapeake Bay watershed covers almost the entire area and draws pollution from a diverse set of sources.