Озерная утка (Oxyura vittata)

Species of bird
Speciesbox
| name = Lake duck
| image = Argentine Blue bill (Oxyura vittata) RWD. jpg
| status = LC
| status system = IUCN3.1
| status ref =
| genus = Oxyura
| species = vittata
| authority = (Philippi, 1860)
| synonyms = Erismatura vittata (Philippi, 1860) Argentine lake duck, or Argentine ruddy duck.

The lake duck grows to Females weigh and males Males can be distinguished from Andean duck (Oxyura ferruginea), a similar species, by being smaller and having a flatter head. It also has the longest penis of any vertebrate in relation to body length. The penis, which is typically coiled up in flaccid state, can reach about the same length as the animal itself when fully erect, but more commonly is about half the bird's length. It has a soft tip and spiny base. ducks have a long corkscrew penis, and the females have a long corkscrew vagina, which spirals in the opposite direction. The males often try to force copulation, but the complex mating geometry allows the females to retain control—most forced copulations do not result in successful fertilization.

Little is known about the lake duck's diet, but it is believed to consist of small invertebrates, seeds, and plant remains. The breeding season varies between countries, occurring from October to January in Argentina. Males produce popping noises and "mechanical rustling noises" for display.

The lake duck is a partially migratory species. It lives in bodies of freshwater with large amounts of vegetation, such as wetlands and lakes. It is very widespread, naturally occurring in Argentina, Brazil, Chile, Paraguay, and Uruguay, and having been introduced to the Falkland Islands. It has a stable population of 6,700–67,000, with no major threats. As of 2016, it is listed as a species of least concern on the IUCN Red List.