Water levels at Lake Titicaca – the highest navigable lake in the world and South America’s largest – are dropping precipitously after an unprecedented winter heat wave. The shocking decline is affecting tourism, fishing and agriculture, which locals rely on to make a living.

“We don’t know what we will do from now until December because the water will keep getting lower,” said 63-year-old Nazario Charca, who lives on the lake and makes a living ferrying tourists around its waters.

Visitors have long been attracted to the blue waters and open skies of South America’s largest lake, which straddles more than 3,200 square miles across the border of Peru and Bolivia.

Sometimes described as an “inland sea,” it is home to Aymara, Quechua and Uros indigenous communities and sits at an altitude of around 3,800 meters (12,500 feet) in the central Andes mountain range, making it the highest navigable lake in the world. The extreme altitude also exposes the lake to high levels of solar radiation, which enhances evaporation and constitutes most of its water losses.