The women – with their long black braids, traditional red bell-shaped skirts, thick woollen jackets and felt bowler hats – hope to set an example for other local residents and tourists who leave tons of garbage by the lake every year.
But their efforts may amount to nothing more than window dressing – wastewater from the surrounding region is contaminating the lake, which many local people rely on for fishing to make a living.
At 8,500 square kilometres, Titicaca – which straddles the border between Bolivia and Peru – is as big as the French island of Corsica.
And at an altitude of more than 3,800 metres, it is the world’s highest body of fresh water that is navigable by large vessels.
The local Aymara people call it a “sacred lake”, – legend has it that from these waters emerged Manco Capac, son of the Sun God, and his wife Mama Ocllo, who then founded the ancient city of Cusco, the capital of the Inca empire.
On the beach of Santiago de Huata, a town on the Bolivian shore of the lake, the women use latex gloves to lift bits of rubbish one by one and put them in huge biodegradable bags.
Such clean-up days are organised once or twice a year to raise awareness about the devastating pollution.
In the dry season, when the water level is low, the scale of the disaster is all the more evident.
“We find plastic, paper, bottles and all types of rubbish,” even “used diapers”, says Helena Condori, a tradeswoman in the Peruvian village of Juliaca on the opposite shore of the lake.
“It hurts me that we are cleaning up what others throw away.”
But she is full of enthusiasm despite the immense task at hand, because “it makes us feel that Peru and Bolivia are more united than ever”.
The women have already cleaned the beach at Puerto Perez, also on the Bolivian side.
But environmentalists and local officials point to a bigger problem: the wastewater now flowing into the lake.
Less than 30 years ago, people could still drink the lake water, but no more.
It is “a problem that is causing serious pollution”, says Fanny Zeballos, an environmental engineer for the non-governmental organisation Agua Sustentable (Sustainable Water).
The organisation supports the clean-up initiative, although Zeballos acknowledges it “will not be enough”.
Bolivian local councillor Reina Silva, who is also taking part in the clean-up day, says the effects of the pollution are all too plain to see.
“Our animals feed on totora (plants) and they die of diarrhoea. Our cows and sheep drink water and die. That’s how we know that it’s polluted,” she said.
“I feel bad – I feel that I’m dying too.”
Agua Sustentable puts together the team of local women and provides the equipment to measure the level of pollution in the lake.
This time, they have collected about 100 kilograms of rubbish.
Juan Jose Ocola, head of the bilateral Lake Titicaca Authority operated by the two countries, says pollution is concentrated on some banks but does not affect the entire lake.
“Lake Titicaca is exposed to a serious pollution problem, as it’s the receptacle for all the pollutants that are produced” in the surrounding area, he says.
The contamination comes mainly from three urban centres, home to some 1.6 million people: Puno and Juliaca on the Peruvian side, and El Alto, next to the capital La Paz, in Bolivia.
Ocola said that although the local women are making “major” efforts, two things are badly needed: the construction of water treatment plants and new garbage dumps.
Peru has already announced the construction of 10 water treatment plants, at the cost of $400 million (B12.881 billion), while Bolivia has earmarked $80mn (B2.562bn) for a similar project in El Alto.