Particles of plastic found in remote waters near the summit of Snowdon are likely being dropped there by polluted rain, scientists say.
A recent study found microscopic beads of plastic in Llyn Glaslyn, near the summit of Wales' highest peak.
Three pieces of microplastic per litre of water were discovered in the lake, with that amount rising to eight by the time the water from the Glaslyn river emptied out into the sea in Porthmadog, the BBC reported.
Environmental experts at Bangor University described the findings as "horrific".
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The samples were collected by environmental activist Laura Sanderson, who swam from the source of the river to the sea - a distance of around 10 miles - collecting water, North Wales Live reports.
She's now due to the UK's 15 national parks to do more research on the phenomenon.
Dr Christian Dunn, a wetland science expert from Bangor University, told the BBC it was "most likely" the plastic was getting into the remote body of water through rain.
He said: "The results are scary when you think that this is at the top of a mountain on a very remote location.
"However, more detailed analysis would almost certainly find more plastic.
"I should be surprised because it's so horrific, but I'm not."
Scientists estimate that plastic pieces - called nanoplastics - which are invisible to the naked eye can circulate in the air and end up returning to land in rainfall.
It is believed that plastic particles of up to five millimetres could also end up in rain.
