Lago Argentino is a lake in the Patagonian province of Santa Cruz, Argentina. It is the biggest freshwater lake in Argentina, with a surface area of 1,466 km2 (566 sq mi) (maximum width: 20 mi (32 km)). It has an average depth of 150 m (492 ft), and a maximum depth of 500 m (1,640 ft).

The lake lies within the Los Glaciares National Park, in a landscape with numerous glaciers and is fed by the glacial meltwater of several rivers, the water from Lake Viedma brought by the La Leona River, and many mountain streams. Its drainage basin amounts to more than 17,000 km2 (6,564 sq mi). Waters from Lake Argentino flow into the Atlantic Ocean through the Santa Cruz River.