Hundreds of fish were found dead in a Co Kildare river leading to fears of toxic chemical contamination.
Residents of Leixlip were left shocked to see fish corpses floating across the River Rye on Wednesday evening.
Over 500 fish have been estimated to have died in the incident.
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Local councillor Joe Neville told Dublin Live: "I was down there myself about 5.30pm on Wednesday evening.
"I saw the fish and everything seemed good. They looked fine. Then I got messages that night at around 11pm that there were dead fish.
"So I went down the next morning. The same river is near my house and you could see all the dead fish."
He added: "They think it’s possibly sewage but you apparently need a huge amount of sewage to kill fish. It normally just dilutes in the water.
"So they’re cautious that there might be another chemical in it that might have caused the deaths of the fish."
Inland Fisheries Ireland is investigating the "serious fish kill incident" and has taken water and fish samples which are currently being analysed.
A spokeswoman said: "Inland Fisheries Ireland estimates that there could be in excess of 500 mortalities of Brown trout plus other fish species in the impacted 2km (approximately) of the river.
"The River Rye Water is an important spawning river for Brown trout and a key spawning channel for a highly sensitive population of Atlantic salmon within the River Liffey catchment area."
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