THE UK's rarest freshwater fish - a relic of the ice age - has been caught on film for the first time during routine survey work in the Lake District.

The fleeting shot of the elusive vendance, an international conservation priority, was captured using a remote-controlled yellow submarine on the bottom of Derwentwater, thought to be its only UK habitat.

The film was taken by the Environment Agency and the Centre for Ecology & Hydrology, who are working to assess how much sediment is building up in the body of water.

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Dr Ian Winfield, from the Centre for Ecology & Hydrology, who led the survey on Derwentwater and operated the submarine, said: “As the day closed, I decided I would go out to the deepest part of the lake which is about 20 metres and drop the submarine in. I’m able to view the images from the submarine’s filming live and was keen to see what fish ‘showed up’.

“Although, the vendace came and went within a matter of seconds, I knew it was a vendace. This was an amazing moment for a scientist, I was not expecting to see one, never mind film one. I knew I had captured for the first time on film the elusive vendace.”

The Environment Agency carries out regular surveys of water quality around the country and over the past five years has worked with farmers, businesses and water companies to improve and protect over 15,000km of rivers, lakes, coastal waters and bathing waters.

Dr Andy Gowans, a fisheries technical specialist at the Environment Agency, said: “It was a unique moment to capture this iconic fish live on film. Seeing the vendace is a good indication of the lake’s health. "Derwentwater is the last native stronghold for these fish in the UK, so maintaining the quality of the water and the lake is vital for their survival.”

The Environment Agency and the Centre for Ecology & Hydrology plan to do further surveying later in the year using more advanced filming technology.