Tucked between snow-capped mountains along the border of Bolivia and Peru, Lake Titicaca was once worshipped by the ancient Inca who proclaimed its deep blue waters the birthplace of the sun.

These days the shores of South America's largest lake are littered with everything from endless bags of soggy waste to discarded hypodermic needles.

Not immediately apparent, but posing a huge threat, are the toxic levels of lead and mercury in the water itself.

The prized tourist destination is slowly deteriorating. A rash of health problems has sprung up among the 1.3 million people who live near Lake Titicaca’s polluted banks.

Increasing concern over the situation prompted promises of official action, and in January the governments of the two countries signed a pact to spend more than $500 million to tackle the problem.

Maruja Inquilla, a local resident, says much of the rubbish comes from nearby cities.

“It’s immensely worrying,” she said. “Why? Because we depend on [it] to live.”

A study carried out in 2014 found mercury, cadmium, zinc and copper in fish that form part of the local diet at higher levels than those advised for human consumption.

The Peruvian president, Pedro Pablo Kuczynski, has pledged to construct ten treatment plants around the lake at a cost of $437 million.