Negros del Agua

According to Austin Whittall, Argentinian folklorist Gregorio Alvarez says that at Lake Caviahue a native named Tranavil saw “black men bathing; they came out to the sandy shore and lay there for a while to rest.”  Whittall writes:

"These 'Negros del Agua' (water blacks) are described as being slightly smaller than men; their aquatic nature is confirmed by their webbed hands and feet. They are evil, and swim in groups looking for canoes to overturn and drown their occupants.

Alvarez also mentions Water Bulls, Lake Horses, and La Sirena inhabiting this lake.

See also Clifden Water Hoses of Ireland.

These beings are some among many that Aquabeasties found on Austin Whittall's wonderful Patagonian Monsters.

More:
Patagonian Monsters: Lake Caviahue - lake of the week
Fernández, C. and López, H. El valle secreto de los Mapuches. Año Cero 126. 07.11.2000. Ed. America Iberica. 11-2000. Online.
Alvarez, G., (1968). El Tronco de Oro. Neuquen: Pehuén. pp. 116 -7.