500 dead fish in Powys river near Llansantffraid-ym-Mechain
Hundreds of fish have died following a pollution incident in a Powys river.
Environment body Natural Resources Wales said about 500 fish, including juvenile salmon and adult brown trout, were found in the River Cain near Llansantffraid-ym-Mechain on Friday.
Water samples and tests of the affected fish have been taken to establish the cause.
Jess Poole, of NRW, said there was no obvious signs of pollution and the water appeared clear.
She added it could take several years for fish populations in the river to recover.
Officers are already investigating the cause of a separate incident which killed about 100 fish on Anglesey.