Driftwood is wood that has been washed onto a shore or beach of a sea, lake, or river by the action of winds, tides, waves, or man. It is a form of marine debris or tidewrack. In some waterfront areas, driftwood is a major nuisance. However, the driftwood provides shelter and food for birds, fish and other aquatic species as it floats in the ocean. Gribbles, shipworms and bacteria decompose the wood and gradually turn it into nutrients that are reintroduced to the food web.