Any duck that obtains its food by diving to the bottom in deep water rather than by dabbling in shallows (see dabbling duck ).
Diving ducks prefer marine environments and are popularly called either bay ducks or sea ducks. Bay ducks (tribe Aythyini, family Anatidae), including canvasback , redhead, scaup , and allied species, are found more frequently in estuaries and tidal lagoons than on the open sea. Sea ducks (20 species in tribes Mergini and Somateriini) include the bufflehead, eiders , goldeneye , mergansers , oldsquaw, and scoters ; some are also or mainly found on inland waters.