The highest lake big ships can navigate sits 3,812 metres up in the Andes

Lake Titicaca sits at roughly 3,812 metres (12,507 ft) above sea level on the Peru-Bolivia border, making it the highest lake on Earth that large commercial vessels can navigate. Spanning about 8,300 square kilometres, it's also South America's largest lake by volume of water.

— Encyclopaedia Britannica, Lake Titicaca