An Taisce has expressed concern about possible contamination of a Co Wicklow reservoir that supplies drinking water to more than half the Greater Dublin area.
The heritage and environmental protection group has claimed supplies at Blessington Lake, also known the Poulaphouca Reservoir, are being put at risk by quarrying and illegal dumping in the area.
Dublin City Council has already expressed concern about a decision by Wicklow County Council to allow further quarrying close to the reservoir.
An Taisce officials are due to visit the area today along with a number of Green Party TDs to assess the situation.
Frank Corcoran, the chairman of the organisation, said he was concerned that Wicklow County Council was failing to honour an agreement to protect the lake.
"There is an agreement between the local authorities to protect the catchment of the Poulaphouca Reservoir," he said.
"(However) Wicklow County Council granted planning permission to a major development which, according to Dublin City Council, represents a threat to the protection of the water supply."