Dredging is an
excavation activity usually carried out underwater, in shallow seas or
freshwater areas with the purpose of gathering up bottom
sediments and disposing of them at a different location. This technique is often used to keep waterways navigable. It is also used as a way to replenish sand on some public beaches, where sand has been lost because of
coastal erosion. Dredging is also used as a technique for fishing for certain species of edible
clams and
crabs (see
fishing dredge).