The river that supplies most of Londonderry with its drinking water was contaminated when water poured into a former illegal landfill site during last week’s floods.
NI Water, however, said the floodwater “will have moved very quickly down river” and “would not therefore be an issue for the abstraction point”.
Fishing organisation Faughan Anglers, however, said the “very essence” of the River Faughan has been threatened.
In a statement, the group said: “Last week’s massive flood breached the flood bank around this lake and now the river and the lake are one, with potentially catastrophic implications for the river, its fish and other wildlife.
“The fact that it supplies the city with drinking water may be of more immediate significance.
“The river’s very essence has been threatened by inappropriate and/or illegal developments along its length.”
A spokesperson for NI Water said: “NI Water is aware that the river bank close to the Mobuoy landfill site was flooded and that river water flooded the old landfill site. Any water which may have come into contact with the old landfill site and washed back into the river during the flooding, will have moved very quickly down river and would not therefore be an issue for the abstraction point.”
NI Water also said both they and NIEA have been “independently monitoring River Faughan” and “no impact has been detected in the river”.
Abstraction from the River Faughan was ceased on August 22 after intake pumps were damaged, NI Water said.
Meanwhile, a plethora of country music stars including Daniel O’Donnell and Nathan Carter are to play a charity concert in Letterkenny, Co Donegal on Saturday in aid of people there who were affected by last week’s flooding.