Which lake, shared by Chile and Argentina, is the largest in Patagonia by surface area?

The lake shared by Chile and Argentina that is largest in Patagonia by surface area is Buenos Aires/General Carrera Lake.

The lake has two official national names: General Carrera in Chile and Buenos Aires in Argentina. Its roughly 1,850-square-kilometre surface is divided between Chile’s Aysén Region and Argentina’s Santa Cruz Province, with most of the lake lying on the Chilean side.

It is a deep, glacially shaped lake in the Andes, reaching about 586 metres at its deepest point. Its western outlet flows through Bertrand Lake into the Baker River and eventually the Pacific Ocean. The famous Marble Caves stand along its Chilean shore.

A common mix-up is to name Lake Argentino or Nahuel Huapi. Both are major Patagonian lakes, but they are smaller by surface area. “Buenos Aires” and “General Carrera” are not two different lakes; they are the Argentine and Chilean names for the same transboundary lake.