The head of the government agency tasked with monitoring pollution seeping from a toxic lake near the River Faughan said it will be a week before he knows if the recent floods have caused pollution to the river.
Environmental campaigners have voiced fears that the recent flood that hit the North West caused a vast toxic lake from an illegal dump on the outskirts of Londonderry to leak into the River Faughan, potentially causing irreparable damage to the flora and fauna it sustains.
The head of waste management at the Northern Ireland Environment Agency, Mark Livingstone, said intensive testing will be carried out at the site now that the flood waters have settled.
Gerry Quinn from the River Faughan Anglers 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 and its fish and other wildlife. The fact that it supplies the city with drinking water may be of more immediate significance to many.
"River Faughan Anglers wish to express their dismay and alarm at this turn of events which has been allowed to happen by the very people charged with protecting the environment, and indeed our drinking water supplies."
Mr Livingstone said he did not share Mr Quinn's fears.
He commented: "We have a monitoring regime at the site for the past two years which specifically looked at run-off, which we have been doing on a regular basis. Since we started that we haven't seen any impact coming from the illegal landfill on the Faughan itself, but since the flooding we initiated a more intensive monitoring programme. We are going to up the intensity of the programme to see if there is any localised impact on the river but we have had to wait until the flood waters dissipated so we could get at the river itself.
"We carry out chemical monitoring but we also carry out seasonal monitoring of the insects that survive in the river which is classified as 'high', which is high quality. We will carry out intensive monitoring of the chemicals now but we will also be carrying out intensive monitoring of the insects which will give us an indication of the impact of this flood. But it will be a week before we know for sure."
As a result of last week's storms, NI Water stopped abstraction from the Faughan because the high water level in the river caused flooding at Faughan pumping station and damaged the intake pumps.
A spokeswoman for NI Water said: "NI Water has been liaising closely with the Northern Ireland Environment Agency (NIEA) who have taken control of the old Mobouy site and have put extensive measures in place to ensure that the River Faughan is protected.
"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 downriver and would not therefore be an issue for the abstraction point."