An art teacher is swimming more than 60 miles in rivers to discover the extent of plastic pollution in some of the UK's remotest areas.
Laura Sanderson is collecting water samples from rivers in three Welsh national parks.
She has already swum 16 miles (26km) along the Afan Glaslyn from near the summit of Snowdon.
The environmentalist fears the results will show that micro-plastics are now in the UK's water source.
Inspired by her travels in the south Pacific, the 37-year-old from Criccieth, Gwynedd, has set about a demanding challenge.
She has swum "from source to sea" along a river in Snowdonia and this month will study rivers in the Brecon Beacons and Pembrokeshire Coast National Park.
However, she fears what the results from her "frog's eye view" may prove.
"I wanted a challenge but I also wanted to find something out that would be useful," she said.
"If we were to find micro-plastics in rivers as high as Snowdonia or in remote areas, we have to ask how did it get there? It must be in the water-cycle. The only way it could get there is by [rain]."
Laura braved snow and icy water temperatures at 2,000ft up Crib Goch peak in Snowdonia, in April.
Stopping at locations along the way to take samples, she swam the length of the river, including four lakes, before finishing at the river's estuary at Porthmadog the next day.
However, even high in the mountains of Snowdonia, water samples were not the only thing Laura gathered.
"I was really surprised to find so many coffee cup lids and plastic bottles near the top of Snowdonia," she said.
"It was upsetting because you'd have thought people out walking would have been more thoughtful.
"There were a lot of beer cans in the lake, which is popular with fishermen. I even found a 1972 Pepsi can under a bridge and lots of car parts, including an entire front bumper and lights.
"Whenever we were close to roads there was a lot of plastic that had probably been thrown out of windows.
"In 100 years people will look back at this time and think we were crazy."
The samples gathered are being studied at the School of Natural Sciences at Bangor University.
Dr Christian Dunn said Laura's swim offered "a fantastic opportunity" to look at the presence of micro-plastics throughout a water catchment.
"It also gave us the chance to see if these tiny pieces of plastic were present in a remote site - a lake at the top of Wales and England's highest mountain - which would be a worrying find."
An area representative for Surfers Against Sewage, Laura also hopes her efforts may have inspired the children at Ysgol John Bright, Llandudno, where she teaches.
She said: "The kids thought I was a bit mad but the best way to educate young people is to show them the impact they have on the environment."