Inland Fisheries Ireland (IFI) is investigating a serious fish kill incident at the Glore River in Kiltimagh, Co Mayo.
Environmental and fisheries officers from the Western River Basin District in Ballina were alerted to the incident on Friday 3 September.
Water and fish samples were taken from the scene and removed for scientific analysis at an independent laboratory.
IFI, the State agency responsible for the protection and conservation of freshwater fish and habitats, estimates that there could be in excess of 500 mortalities of young salmon and trout.
Investigations are ongoing and IFI says it not in a position to comment on the cause of the fish kill at this stage, pending further analysis of samples taken.
The Glore is described as an important spawning river for trout and salmon within the Moy catchment area.
This incident comes just says after Northern Ireland experienced its third fish kill in as many months — two of them on the same river in Co Antrim.
