Driftwood is formed when a tree or large tree branch washes into the ocean (or another large body of water), usually because of strong winds, as in a storm, or due to flooding. The tree dies and the dead wood shelters and feeds fish, birds, and other aquatic species, as it floats in the ocean. Gribbles, shipworms, and other bacteria decompose the wood and gradually turn it into nutrients that are reintroduced to the food web. Sometimes, the partially decomposed wood washes ashore and shelters birds, plants, and other species. The driftwood can become part of the foundation of sand dunes.
Driftwood carried by Arctic rivers was the main, or sometimes only, source of wood for some Inuit and other Arctic populations living above the treeline until they came into regular contact with European traders.
Many people use driftwood as parts of decorative furniture or other art forms, and it is a popular element in the scenery of fish tanks.
One famous piece of driftwood is the "Old man of the lake" in Crater Lake, Oregon. It is a full sized tree that has been bobbing in the lake for more than a century. Due to the cold water temperature of the lake, the tree has been well preserved.