The case against Roscommon County Council for constructing an overflow pipe at Lough Funshinagh in south Roscommon is due before the High Court today.
Friends of the Irish Environment successfully secured an injunction earlier this month which forced the local authority to suspend the works, with locals fearing that their homes will flood this winter.
Hundreds of acres of farmland are already underwater with the levels of the former turlough now 2.5 to 3 meters higher than normal for this time of year.
FIE is raising concerns over potential damage to the Special Area of Conservation.
This is contested by locals who say that as well protecting people's homes and livelihoods, is also aimed at restoring the natural habitat which has been destroyed by flooding.
The case is due to be mentioned in the High Court today with a full hearing expected to proceed next month.
