Inland Fisheries Ireland (IFI) says it is investigating a “locally significant” fish kill on the River Glyde in Co Louth.
The incident occurred in the vicinity of Tallanstown, some 13km south-west of Dundalk.
Fisheries environmental officers have been on site since Tuesday evening (2 June) to investigate.
Species of fish discovered dead include adult and juvenile Atlantic salmon, eel, brown trout, pike and coarse fish.
Samples taken at the river have been sent for laboratory analysis.
A considerable stretch of the river is affected, and the estimated number of fish mortalities is currently being assessed, IFI says.
The agency confirms that it is actively investigating the cause of what it calls a “harmful ecological event”.
It says a definite line of enquiry is being pursued, and local authorities have been notified.
Monitoring and assessment of the impact will continue to be undertaken by IFI staff, the agency adds.
