This is only the third site in the UK, that the microscopic organisms, named Cytherissa lacustris, have been found to be living in the UK; they have also been found at Loch Assynt in Scotland and a site in north England.
A species of creature called ostracods, the small crustaceans only grow to about a millimetre in length.
David Horne, professor of micropalaeontology at Queen Mary University of London, who made the discovery in Loch Leven, near Kinross, says the creatures are relatively common in other countries around Europe and in Canada but that they are quite rare in the UK.
Prof Horne began his investigation into the possibility of a population of the ostracods living in the loch following a visit to the Discovery Museum in Newcastle upon Tyne.
The scientist told the BBC: “I came across a microscope slide containing ostracods collected from Loch Leven in June 1890, among which were several specimens of Cytherissa lacustris.
“In some I could see appendages protruding from between their shells, a clear indication that they had been alive at the time of collection.”
Earlier this year, the professor was able to take his own samples from the loch and has been analyising them in a bid to assist his research into understanding winter and summer temperatures experienced by early humans in the British Isles.