The cause of the deaths of hundreds of bream in Lough Derg is expected to be known the next few days when results of scientific tests will be available, according to the Shannon Regional Fisheries Board.
Mr Eamon Cusack, chief officer, said the dead fish had been found in the Whitegate/ Scarriff and Portumna/Terryglass areas. The board was working with the ESB's adviser on coarse fish health, Dr Kieran McCarthy of UCG, to establish the cause.
He said the board was conscious of the economic benefits to the Shannon catchment of coarse angling through tourism angling and has requested the Department of the Marine and the Central Fisheries Board to become actively involved in the investigations into the deaths.
Ms Iva Pocock, a water campaigner with Greenpeace Ireland, said that because the fish were found dead there was speculation that it was a virus.
"The ecology of Lough Derg, as the last lake on a river which has been declining in water quality over the last 20 years, is severely damaged. While funds have been made available to tackle sewage pollution in the Lower Shannon catchment, there is no integrated plan to reduce agricultural sources of pollution at the same time. What is needed is a comprehensive action plan to reduce all sources of pollution into the Shannon system," she said.