The river that forms part of the Coastal Plains boundary is Savannah River.

The Savannah River forms part of the Coastal Plain's boundary, serving as a natural divider between Georgia and South Carolina. Stretching approximately 300 miles, this river plays a crucial role in the region's ecology and economy. It provides essential water resources for agriculture, industry, and recreation, supporting local communities along its banks. The Savannah River is also significant for its historical importance, as it was a key transportation route during the colonial era. Today, it attracts tourists for its scenic beauty and recreational activities, such as fishing, boating, and hiking, highlighting its ongoing relevance to the Coastal Plains.