Dredgers

Dredging is an excavation activity usually carried out underwater, in shallow seas or freshwater areas, to gather up bottom sediments and widen.
Dredgers are vessels with excavation tools used for removing sand and other types of deposits from the seabed. Dredgers are used for several purposes, such as making shallow coastal areas navigational, deep-sea mining etc.
Dredgers are mainly classified into two types:
Mechanical dredgers
Hydraulic dredgers