A "wipeout" is how an angler has described a fish kill which is believed to have affected thousands of fish across miles in Co Louth.
Inland Fisheries Ireland (IFI) is currently investigating what it calls a "locally significant" fish kill on the River Glyde, near Tallanstown.
Officers have been on site since Tuesday night investigating the incident.
Dead fish include adult and juvenile Atlantic salmon, eel, brown trout, pike and coarse fish, and samples taken at the river have been sent for laboratory testing.
In a statement, IFI said: "A considerable stretch of the river is affected, and the estimated number of fish mortalities is currently being assessed.
"IFI is actively investigating the cause of this harmful ecological event. 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."
PRO of the Dee and Glyde Fishing Development Association Jim Curley told LMFM Radio's Late Lunch that he had never before seen anything like it.
"I have been associated with this club for 40 years and I've never in my lifetime seen anything like it. To see salmon, sea trout, brown trout, pike, minnows floating with no hope, they were gone.
"It's a complete wipeout of all fish stocks. We won't really know the full details for days.
"This was one of the most important amenities in the area. The Dee and Glyde Fishing and Development Association had fishing rights on both the Glyde and the Dee but the detriment is going to be serious for the club.
"Who would want to fish a river in the condition that it's in? You're talking about miles and miles here, and everything in the wake of this has been killed."
Curley believes it could take years to restock and repopulate the river.
