Ducks swim with webbing stretched between the toes, a single continuous membrane. Coots and grebes instead have lobate feet: each toe is individually flanked by broad, hinged flaps of skin. On the power stroke the lobes flare outward and press water; on the return they collapse against the toe, cutting drag.
The arrangement is a compromise that suits a bird moving between water and land. Webbing is awkward on mud and matted vegetation, whereas separate lobed toes can be lifted and placed like walking toes, letting coots forage on banks, lawns and reedbeds as readily as they dive. Coots dive for pondweed and invertebrates, kicking up from the surface with a small forward jump.
The coot is often filed with the ducks by sight. It belongs to the rail family, Rallidae, and the resemblance to a duck is convergence on a swimming lifestyle rather than close relationship.