A river delta is a landform that occurs at the mouth of a river, where it meets a body of water like an ocean or a lake. As the river flows, it carries sediment, which is deposited when the water slows down. This accumulation of sediment creates new land, often in a triangular or fan shape. Deltas are important ecosystems that support diverse wildlife and plant species. They also provide fertile soil for agriculture and serve as natural buffers against flooding. Famous examples of river deltas include the Mississippi River Delta in the United States and the Nile Delta in Egypt.