The hooded merganser (Lophodytes cucullatus) is a species of fish-eating duck in the subfamily Anatinae.

The bird is striking in appearance; both sexes have crests that they can raise or lower, and the breeding plumage of the male is handsomely patterned and coloured.

The hooded merganser was formally described in 1758 by the Swedish naturalist Carl Linnaeus in the tenth edition of his Systema Naturae under the binomial name Mergus cucullatus.

[2] Linnaeus based his account on the "round-crested duck" that had been described and illustrated by the English naturalist Mark Catesby in the first volume of his The Natural History of Carolina, Florida and the Bahama Islands that was published between 1729 and 1732.

[4] The hooded merganser is now the only species placed in the genus Lophodytes that was introduced in 1853 by the German naturalist Ludwig Reichenbach.

The adult female has a greyish-brown body, with a narrow white patch over the lower breast and belly.

A smaller year-round range extends from Washington state and southern British Columbia to northern Idaho.

They also breed to some extent in regions from Missouri to southern Canada and from Nova Scotia to eastern North Dakota and Saskatchewan, migrating when necessary to avoid winter conditions.

Once they leave the nest, the young are capable of diving and foraging, but remain with the female for warmth and protection.

Because these waterfowl are cavity nesters, they require mature trees in which suitable nesting sites are likely to be found.

[18] Because of their high reliance on aquatic prey, hooded mergansers are very susceptible to harm from many types of pollution, some of which are poisons that accumulate in the food organisms, directly poisoning predators high in the food chain, and some of which simply reduce the populations of their prey.