Separate investigations are underway to determine the cause of a serious incident in North Clare in which up to 2,000 fish have died.
Inland Fisheries Ireland says the fish kill happened on the Ballymacraven River in the past week.
Inland Fisheries Ireland and the EPA first became aware of an ecological issue in recent days when a member of the public informed them of a rusty red colour on the Ballymacraven River, near Ennistymon.
Up to 2,000 fish have since been discovered dead, incliding a large number of eel, along with salmon, trout, rudd and flounder of all ages.
The fish kill spread for 2.6 kilometres to where the Ballymacraven River meets the Inagh River, which is an Special Area of Conservation.
Local man Paudie Fahy witnessed the scenes over the weekend and he says the sight was “sickening”.
The IFI, which is the State agency responsible for the protection and conservation of freshwater fish and habitats has undertaken water sampling in recent days to assess the quality of the water.
It says, however, it’s not in a position to confirm the specific cause of this fish kill at this early stage.
IFI Spokesperson Jane Gillernan says investigations are continuing.
Uisce Éireann says it’s currently liaising with Inland Fisheries Ireland as part of this process, and that the processes and outputs from the Ennistymon water treatment plant are being closely monitored as part of this.
Inland Fisheries Ireland, meanwhile, is reminding the public they can report instances of fish kills, pollution or illegal fishing nationwide by calling its confidential 24/7 number 0818 34 74 24.
