Natural Resources Wales staff have been on site at the Clywedog river near Wrexham following a ‘fish kill’ incident yesterday.
Natural Resources Wales have said: “Our officers have been on site at the river Afon Clywedog following a pollution incident last night that has killed a significant number of fish.
“They attended the site at 11pm and initially found about 50 dead fish in a 500m stretch, but the river looked clear and they were unable to locate the pollution source.”
Officers have returned to the site this morning to continue their investigations.
Natural Resources Wales added “Please report any incidents of pollution or fish kill to our incident hot line on 03000 65 3000.”