Inland Fisheries Ireland are investigating a fish kill on the river Vartry in Wicklow.
It is understood that the problem was first noticed this morning and that large quantities of dead fish have been seen flowing downstream all day.
A statement on the Wicklow County Council website said that they have temporarily shut off raw water supply intake from Vartry River to our Water Treatment plant at Cronroe as a precaution.
Local sources said reports had been received of dead fish as high up the river as Roundwood, and as far down the river as Ashford.
It is also understood that a dead heron has also been found, although it is not clear if this is related to the fish kill.
A source in Inland Fisheries Ireland confirmed the matter is under investigation, but would not speculate about how extensive the problem is or what the cause might be.