Galletué Lake in the context of Araucaria araucana

The Biobío River (also known as Bío Bío or Bio-Bio) is the second largest river in Chile. It originates at Icalma and Galletué lakes in the Andes and flows 380 kilometres (236 mi) to the Gulf of Arauco (in Spanish) on the Pacific Ocean.

The major tributaries of the river are the Malleco and the Laja. The river is Chile's second-longest river (the longest being the Loa River) and the Biobío basin is Chile's third largest watershed, after the Loa and Baker basins. The river is also the widest river in Chile, with an average width of 1 kilometre (0.6 mi). In the Metropolitan area of Concepción, four bridges cross the river: Biobío Railroad Bridge (1889), Juan Pablo II Bridge (1973), Llacolén Bridge (2000) and Bicentennial Bridge (2010).

Icalma Lake is a lake of glacial origin located in the Andes of the La Araucanía Region of Chile. A hamlet on the southern shore of the lake is also called Icalma. About 3 kilometres (1.9 mi) from the hamlet is Icalma Pass, 1,307 metres (4,288 ft) in elevation and on the border with Argentina. The pass is traversed by a road, unpaved in Chile in 2017 and sometimes impassable during the Southern Hemisphere winter due to heavy snows. Icalma Airport is located 9 kilometres (5.6 mi) northeast of the hamlet and some 8 kilometres (5.0 mi) from the border with Argentina.

Icalma Lake is connected to the Laguna Chica de Icalma (Little Lake of Icalma) by a short stream about 300 metres (980 ft) long. The two lakes together have a surface area of 11.7 square kilometres (2,900 acres). Icalma Lake drains northeastwards by way of a 10 kilometres (6.2 mi) long river named Rukanuco. Icalma Lake and nearby Galletué Lake are the sources of the Bio Bio River.