Lake General Carrera/Buenos Aires, Binational glacial lake in Patagonia, Argentina and Chile.

Lake General Carrera/Buenos Aires covers 1,850 km², with 970 km² in Chile's Aysén Region and 880 km² in Argentina's Santa Cruz Province. Its western basin reaches 586 m deep, and the shoreline includes the Marble Caves, Marble Chapel and Marble Cathedral, formed in marble monoliths by wave action over 6,200 years.

The basin formed thousands of years ago when massive glaciers during the Ice Age shaped the land and carved deep valleys. As the ice retreated, water filled the depression and created the lake we see today.

The Aonikenk name Chelenko means "stormy waters", though a study of 26 late-18th and 19th-century maps found explorers could not agree which lake the name referred to, and indigenous guides deliberately obscured their routes. Mapuche families were recorded at Cholila by 1896; settlers of Argentine, Chilean and European origin reached the shores between 1900 and 1925.

The main Chilean entry is at Puerto Ingeniero Ibáñez, on the northern shore, where a car ferry crosses to Chile Chico. On the Argentine side, Los Antiguos sits beside the lake and Perito Moreno lies a few kilometres inland. The Carretera Austral, opened in the early 1990s, ended the Chilean shore's long isolation.

The Marble Caves, Marble Chapel and Marble Cathedral sit on the shoreline midway along the lake, a group of caverns, columns and tunnels cut into marble monoliths by wave action over the last 6,200 years. The rock is marble, not calcium carbonate cliffs, and boats leave from Puerto Río Tranquilo to reach them.