The Smew (Mergellus albellus) is a species of duck that is intermediately placed between mergansers and goldeneyes. It is the only member in its genus Mergellus, which is sometimes grouped with the Mergus genus of mergansers. However, it is most likely closer related to the goldeneyes, and has interbred with the Common Goldeneye (Bucephala clangula).

The Smew is found in the northern taiga (coniferous evergreen sub-arctic forests) of Europe and Asia. Its habitat is densely wooded forests around fish-rich lakes and slow-moving rivers. It migrates toward sheltered coasts or inland lakes of the Baltic Sea, the Black Sea, and northern Germany. Some individuals may reach Great Britain. It prefers areas of lakes around the edges, often under small trees.

The male Smew is unique in appearance and looks very black-and-white in flight. The females and immature males are gray birds with chestnut foreheads and crowns, and can be confused at a distance with the
Ruddy Duck. It has oval white wing-patches in flight. The Smew’s bill has a hooked tip and serrated edges, which help it catch fish when it dives for them.

The Smew breeds in May and the female lays 6 to 9 cream colored eggs. It nests in holes in a tree, such as old woodpecker nests. It is shy and flushes easily when disturbed. The Smew is not considered threatened by the IUCN.