Some 800 fish have been released in a bid to protect a species under threat of extinction in north Wales.
The Arctic char were reared from eggs harvested in December 2009 from fish threatened by harmful algae at Llyn Padarn, Llanberis, Gwynedd.
Their release into Llyn Crafnant, near Trefriw, Conwy county, will establish a back-up population while the water quality at Llyn Padarn is improved.
A study into the causes of the 2009 algal bloom is due to end in December.
The young char, also known as torgoch, being released into Llyn Crafnant have been hatched and raised from eggs collected from 25 adults caught at Llanberis in December last year.
They have been cared for at the Mawddach Hatchery, near Dolgellau, for the past 11 months.
The Arctic char can be found only in a few cold, deep lakes in north Wales where they have developed into distinct populations.
Environment Agency Wales (EAW) said the 2009 blue green algae problem was caused by what was dubbed the "perfect storm" due to a combination of relatively high phosphates, weather conditions and high water temperature.
The Countryside Council for Wales (CCW) concluded that its char population was in imminent danger of extinction and the plan for the Llyn Crafnant release was formulated.
This year, EAW said, no blue green algae has been detected in the lake.
But the two bodies are working with Gwynedd council, Dŵr Cymru Welsh Water and First Hydro Company on a long-term project to improve water quality at the lake for both wildlife and people.
The study of Llyn Padarn, which has examined it during each of the four seasons, will help the partnership draw up an action plan to tackle the cause of the algal blooms.
Discharge consents at Llanberis sewage treatment works have already been tightened to control the quality of effluent entering the lake, said EAW.
A forum of local businesses and community groups has also been established to provide advice and feedback on the work.
David Edwell, EAW's area manager, said Llyn Padarn was a vital part of the community and economy in north Wales.
Trying to find a solution to avoid a repeat of the algal bloom of 2009 was one of the agency's top priorities, he added.
"It is not only businesses that rely on the lake, the Arctic char also need a good habitat to thrive," said Mr Edwell.
"Setting up the secondary population is a safety net - but we are determined to find a way to improve the conditions at Llyn Padarn so they can continue to inhabit the lake."