Underwater monitoring by Natural Resources Wales specialists is checking on the amount of Arctic charr heading upstream from Llyn Padarn to spawn.
The fish were monitored using sonar over a six week period at the end of last year when the charr traditionally migrate up the Afon y Bala to spawn.
It picked up more than 26,000 traces of smaller fish, which could be Arctic charr, brown trout or small sea trout, moving between the lake and the river and back.
Typically the charr migrate into the river to spawn at night and return to the lake before daylight.
The sonar also picked up almost 800 traces of larger fish, usually salmon or sea trout, in the same area.
Four underwater cameras, installed for two weeks covering the same area, recorded 560 fish passing through. Over 200 of these were positively identified as 48 Arctic charr, 42 salmon, 105 brown trout and 8 sea trout.
The rest (almost 330) were less than 50cm long and are likely to be either Arctic charr or brown trout. It is not possible to distinguish between them with 100% certainty.
This monitoring was part of on-going work to protect the Arctic charr and improve water quality at Llyn Padarn.
Natural Resources Wales is taking action to protect this rare ice-age fish as it has been in decline over the last 30 years.
8000 young charr have already been released into Llyn Padarn in the last four years to boost the population with a further 1700 to be released later this year. 7000 charr have also been released into Llyn Crafnant in the Conwy Valley to establish a ‘back-up’ population.
Stocking Arctic charr into the lake, and into the secondary lake in the Conwy Valley, has been established to reduce the risk of the population becoming extinct as the numbers have reached dangerously low levels.
Llyn Padarn is now a designated EU bathing water due to its popularity and is being tested every week during the bathing water season (May – September).
So far, five samples out of the twenty that will be taken over the season have found that the water meets the ‘Excellent’ standard which is the highest mark for cleanliness.
Since a major blue-green algal boom in 2009, Natural Resources Wales has taken action to tighten permits for nearby sewage treatment works at the lake which, along with other work by Dŵr Cymru Welsh Water, has improved conditions at the lake.
Tim Jones, Director for north and mid Wales, Natural Resources Wales said:
“The result of our monitoring is encouraging but the amount of charr migrating is still well below the numbers a lake of this size can support.
“It is good to see that water quality at the lake has improved and reducing the risk of an algal bloom - which had such a dramatic impact on the local economy in 2009.
“What this shows us is that we must keep up with the work we have carried out in the last five years to improve Llyn Padarn for to benefit of the local community, the local economy and the wildlife that lives there.”