The large body of water that is part of the Coastal Plains is Chesapeake Bay.

Chesapeake Bay is a prominent large body of water located within the Coastal Plains, known for its ecological and economic significance. Spanning parts of Maryland and Virginia, it is the largest estuary in the United States, where fresh and saltwater mix, creating diverse habitats for a variety of wildlife. The bay supports vital fisheries and recreational activities, contributing to the local economy. Its rich history and cultural heritage are evident in the surrounding communities, which celebrate the bay's resources through seafood festivals and conservation efforts. Chesapeake Bay's health is crucial for maintaining the region's biodiversity and environmental sustainability.