Anglers who argued not enough was being done to protect an endangered fish in a Snowdonia lake have lost a judicial review against Natural Resources Wales.
The fishermen claimed treated discharge from a water treatment works had degraded the quality of Llyn Padarn at Llanberis.
They said the annual catch of Arctic charr there had dropped and the regulator had not protected them.
But Mr Justice Hickinbottom said there was no evidence of this.
He said since 2011, to overcome the problem of a lack of spawning grounds, the lake had been restocked with young fish.
“There is no evidence of a decline in the charr population in Llyn Padarn since 2007 and there is evidence the population of adult charr are now at a level higher than 2005 and increasing, which is at least suggestive that the water is not hostile to charr,” the judge added.
The judicial review proceedings in Caernarfon had been brought by the Seiont, Gwyrfai, and Llyfni Anglers Society, represented by a body called Fish Legal – an umbrella organisation for fishing groups.
Lawyers challenged Natural Resources Wales’s claim that no environmental damage, except an algal bloom six years ago, was caused from raw sewage and treated effluent discharged by Welsh Water.
Speaking after the case, Welsh Water said it had invested £3.6m at the works since 2010 to meet tighter standards set by NRW which helped make it Wales’ first designated freshwater bathing lake.
Sian Williams, head of operations for NRW, added: “We have always tried hard to work in partnership with the angling club to address their concerns and will continue to do so.”
Huw Hughes, secretary of the Seiont Gwyrfai and Llyfni Angling Society, said they were disappointed by the decision.