An investigation has been launched into water pollution in the river.
An investigation has been launched following a serious fish kill incident at the River Rye Water in Leixlip, according Inland Fisheries Ireland, the state agency responsible for the protection and conservation of freshwater fish and habitats.
Water and fish samples were taken from the scene and removed for scientific analysis at an independent laboratory, said Inland Fisheries Ireland.
It estimates that there could be in excess of 500 mortalities of Brown trout plus other fish species in the impacted 2km (approximately) of river.
It said investigations are ongoing and Inland Fisheries Ireland is not in a position to comment on the cause of the fish kill at this stage, pending further analysis of samples taken.
Environmental and Fisheries Officers from the Eastern River Basin District in Dublin were alerted to the incident on the evening of Wednesday, June 8th.