Rupanco Lake, Natural lake in Los Lagos Region, Chile

Rupanco Lake lies in Osorno Province, Los Lagos Region, split between the communes of Puyehue in the north and Puerto Octay in the south. It covers 230 km², making it the second-largest lake in the region after Llanquihue, and stretches 42 km from east to west at 70 m above sea level. Its elongated shape winds between Andean summits, including the Puntiagudo and Casablanca volcanoes.

The lake was known as Llauquihue until the geographer Guillermo Döll proposed the name Rupanco in 1852 to avoid confusion with Llanquihue. Colonisation of the eastern sector began around 1930 with the Colonia Agrícola Rupanco, which started with 56 settlers on 66 parcels totalling 23,228 hectares. The Hotel Termas de Rupanco opened on the northern shore in the late 1940s and was destroyed by an avalanche during the 22 May 1960 Valdivia earthquake.

The name Rupanco comes from the Mapudungun Reipún-ko, "stirred water"; until the mid-19th century the lake was called Llauquihue, and geographer Guillermo Döll proposed the current name in 1852. On the southwest shore stands Hacienda Rupanco, a large dairy-farming estate. Each summer the Club de Pesca y Caza de Osorno holds a fishing championship on the lake.

Access is by a paved road from Osorno, 52 km away; three routes reach the lake from the north, and a road follows the southern shore to its eastern end. Shore settlements include Pellinada, Chacay, Piedras Negras, El Islote, El Poncho, Las Vegas and Puerto Chalupa. Summer water temperatures run about 9 to 22 °C.

The eastern end of the lake was settled from the early 1930s through the Colonia Agrícola Rupanco, which began with 56 settlers on 66 parcels totalling 23,228 hectares. On 22 May 1960 the Valdivia earthquake sent over 100 million cubic metres of earth sliding from nearby hills into the lake, producing a wave up to ten metres high.