A survey of mountain lakes from Donegal to Kerry has uncovered new populations of the rare Arctic Char, a salmon-like fish that lives only in the purest of waters.
However, the scientist leading the survey has warned that "worrying levels" of water abstraction from mountain lakes by local authorities endangers the unique populations of rare fish.
Scottish fisheries biologist Mr Ron Greer has also warned about the introduction of "exotic species" such as rudd, which have been found in lakes where previous populations of char were recorded.
Rudd were found to have replaced char in the Upper Lake in Killarney, a previous stronghold of the Arctic char, the survey, carried out in conjunction with the Irish Char Conservation Group, found. No char were found in the Killarney lake, widely regarded as the most unpolluted of the three Lakes of Killarney. This was the second time the lake had been surveyed, Dr Fran Igoe, a scientist with the char group, said.
New populations of char have been discovered at Cloon lake in Co Kerry and at Lough Derrianna near Waterville, where they were thought to have been extinct.
At Lough Fad (East) in Co Donegal, on the Inishowen peninsula, the group discovered the lake only contained char.
"It's the first of its kind in Ireland," Mr Greer explained. Elsewhere, only two lakes in Britain, one in Scotland, have this phenomenon.
Lough Salt, also in Donegal, was found to have char.
However, abstraction levels for water supply for domestic houses from these lakes was "worrying" and needed to be looked at, Mr Greer said.
Lough Guitane in Kerry, the county's main public water supply, was also suffering from high levels of water extraction and the damage this was doing to the lake's fish population had yet to be assessed, Mr Greer said.
To discover new populations in a modern country was "astounding", he added.
Char have been in Ireland since the Ice Age when they became locked in mountain lakes and changed from being migratory fish, like their cousins the salmon, to remaining in freshwater. Kerry was a stronghold of char, he found.