On the shores of Lake Issyk Kul in mountainous Kyrgyzstan, a group of divers show off their haul for the day -- a boat engine, car tyres, bottles, clothes and plastic items.

"We would love to dive and not find any waste," said Anvar Shamsutdinov, the moustachioed 59-year-old leader of a dozen-strong team of volunteer scuba enthusiasts.

"The beach looks clean but people don't realise what's underwater," he said, as tourists stopped to look.

Surrounded by snowy Central Asian peaks over 4,000 metres (13,000 feet) tall, Issy Kul is the second largest high mountain lake in the world.

The year's brief but intense summer high season has just got under way in this picturesque region of the former Soviet republic, where the nearest seaside is thousands of kilometres (miles) away.

But the flow of visitors and the rubbish they leave behind are endangering this vast lake known as the "pearl of Kyrgyzstan" -- whose pristine waters are highly vulnerable to pollution.

The lake area is a UNESCO heritage site, a home for wolves and eagles, and a wintering ground for tens of thousands of migrating waterbirds.

"In 2014, we were doing some underwater orientation and we realised the situation under water was terrible," Shamsutdinov said.

"So we decided to clean up the lake," said the diver, who estimates he has collected 20 tonnes of waste since creating his association "Clean Issyk Kul".

- For future generations? -

On a visit to the lake earlier this year, Kyrgyz President Sadyr Japarov cautioned about the dangers and urged the public to preserve the lake.

"Why is there so much indifference and insensitivity towards our beloved lake?" he asked. 

"Cleanliness is about cleaning up. It's about not dumping rubbish in the first place."

The emergency situations ministry has also sent divers to help Shamsuddinov and his team of volunteers.

These initiatives are all welcomed by Gulzam Satybaldieva, who runs a shop on the beach at one of the lake's main resorts, Cholpon-Ata, and is grateful to "divers who are sensitive to environmental problems".

"If tourists and (local residents) followed their example, we would be able to pass on a clean lake to future generations," she said.

But in Kyrzgystan, as in the whole of Central Asia, the recycling industry suffers from underinvestment and the problems at Issyk Kul point to broader environmental issues, like smog from coal burning and nuclear waste lingering from the Soviet period.

"We haven't cleaned the lake in 30 years -- since independence" from the Soviet Union, said Aidar Kaptagayev, a diver from the emergency situations ministry. 

He has been diving in the lake since March at depths of up to 40 metres to get rubbish out.

- 'Bringing shame' -

Apart from petrol and waste from factories and other industrial facilities, which put at risk the lake's plant life, plastic and fishing nets endanger animals.

But environmental awareness is slow to take hold.

Shamsutdinov said he and his team are sometimes even accused of "bringing shame" on the country by showing how much waste is thrown in the water.

The manager of a cafe on the lake shore, Ruslan Myrzalyev, said that "some tourists don't really respect rules on waste, despite requests".

Vera Argokova, a 62-year-old tourist from Russia's Altai region, said she was particularly careful.

"We do not bring food onto the beach, only a bottle. We want everything to stay clean," said Argokova, who was staying at the "Blue Issyk Kul" sanatorium, decorated with Soviet-era statues including one of Lenin.

"We don't want to be relaxing surrounded by rubbish."

str-bk-dt/jbr/gil