5.3. Salt Marshes Rivers flowing into estuaries have carried heavy loads of silt over long periods of time. The silt is deposited where freshwater meets saltwater. This creates extensive mud banks. In many of these places salt marsh plants begin to grow quickly. Rising and falling tides in the salt marsh provide nutrients to the plants and they grow quickly. A well-developed "salt marsh" is more productive than a good hay or wheat field. Salt marshes, especially ones around the Bay of Fundy, support a rich variety of fish and birds.