The term 'River MARSH' can be broken down into two words: 'River' and 'MARSH'. A river is a large natural stream of water that flows through a channel in the surface of the ground. A MARSH is an area of low-lying land that is flooded with water, either permanently or seasonally, and dominated by grasses, rushes, reeds, and other aquatic plants. The crossword solution for this term is 'BAYOU', which is a slow-moving body of water found in the southern United States, typically in low-lying areas near rivers and streams.