Lake Todos los Santos is located in the Andean pre-mountain range in the Araucanian lake district of southern Chile within the latitudinal range of 39-42S. Lakes in the district have many biotic and abiotic characteristics in common, but differ in the extent of their oligotrophy.

L. Todos los Santos has a surface area of 178.5 km2 and a large volume owing to its great depth reaching a maximum of 337 m. The catchment area of the lake is fairly wide, being 17 times as wide as the lake surface. Its origin is both glacial and volcanic. During in the Ice Age, two glacier arms, one flowing down southward through the present Negro River valley and the other in the opposite direction through the Blanco River valley, converged in the central valley and advanced westward excavating the tertiary valley to form the depression now occupied by Lakes Todos los Santos and Llanquihue. After the disappearance of the ice, the action of Osorno and Calbuco Volcanoes divided the two lake basins with volcanic matters. Matters from Tronador Volcano also reached the lake via Blanco River glacier.

The lake is warm monomictic and oligotrophic. The concentration of major nutrients are low. The highest carbon assimilation rate per unit amount of chlorophyll occurs in winter, but the primary production reaches its highest level at the beginning of summer, though the productivity itself is low (1, 2).