The Pascagoula River is a river, about 80 miles (130 km) long, in southeastern Mississippi in the United States. The river drains an area of about 8,800 square miles (23,000 km²) and flows into Mississippi Sound of the Gulf of Mexico. The Pascagoula River Basin is managed by the Pat Harrison Waterway District.

The Mississippi Sound is a sound along the Gulf Coast of the United States. It runs east-west along the southern coasts of Mississippi and Alabama, from the mouth of the Pearl River at the Mississippi-Louisiana state border to the Dauphin Island Bridge, a distance of about 90 miles (145 km). The sound is separated from the Gulf on its southern side by the Mississippi–Alabama barrier islands: Cat, Ship, Horn, West Petit Bois, Petit Bois, and Dauphin. Ship, Horn, West Petit Bois and Petit Bois Islands are part of the National Park Service's Gulf Islands National Seashore. Those islands separate the sound from the Gulf of Mexico. The sediment of the islands was created partly by the ancient Mississippi River when the St. Bernard Lobe of the Mississippi Delta was active over two thousand years ago. The expansion of the St. Bernard subdelta slowly isolated the Mississippi Sound from ocean dynamics of the open Gulf of Mexico.