Shoal of 100 Arctic charr seen in Llyn Padarn
Underwater monitoring has revealed one of the largest shoals of Arctic charr ever seen in Llyn Padarn, Snowdonia.
About 100 of the fish were recorded in one shoal, as part of Natural Resources Wales' (NRW) annual count to see how many head upstream from the lake to spawn.
They were monitored at the end of last year, when they traditionally migrate up Afon y Bala.
As well as underwater cameras, NRW used a sonar acoustic device.
This was essential to monitor the fish in murky water and in the dark - Arctic charr usually migrate at night and return to the lake before daylight.
Anglers who argued NRW had failed to protect Arctic charr at the Gwynedd lake lost a judicial review in December 2015.
NRW said that over the last few years, several measures had been taken to improve the environment in Llyn Padarn and conserve the fish.
A spokesman said young charr, reared in NRW's hatchery from eggs taken from Llyn Padarn's charr population, have been released into the lake to boost the population.
Work has also been done to improve water quality in the lake, which is now graded as excellent.
Sian Williams, NRW's head of north west Wales operations, said: "Gathering evidence like this is a vital part of our work.
"I'm delighted that measures to conserve and enhance Llyn Padarn and its Arctic charr are now bearing fruit, with improved spawning runs in Afon y Bala."