The Merganser Duck, also known as the SMEW (4 letters), is a species of duck found in the Northern Hemisphere. It is a medium-sized diving duck with a long, thin bill and a crest of black and white feathers on its head. The Merganser Duck is an excellent swimmer and can be found in rivers, lakes, and estuaries. It feeds mainly on fish, but will also eat crustaceans, mollusks, and aquatic insects.