These birds prefer fresh water and are seldom found near salt water.

The male has a dark green head that appears almost black. The female has a crest on her head and a white throat. Both have a thin, red, hooked bill with sharp teeth along the edges. These teeth help them catch their swimming prey. The teeth also help them keep a grip on slippery fish.

Mergansers dive underwater to catch fish, their preferred prey. They can swim well and quickly pursue prey underwater. Mergansers also eat aquatic insects.

The call is a low, short quack.

They build their nests on the ground or in crevices of trees. Mergansers are commonly seen flying along some river canyons. They sometimes skim low over the water, usually in pairs. White wing patches are visible when they are in flight. Mergansers prefer open water.

The webbing on their feet sometimes shows in the tracks.