The Environmental Protection Agency has blamed a Donegal County Council treatment for being a significant cause of the decline in the pearl mussel population.
In a report, the Environmental Protection Agency says an immediate upgrade of the Kilmacrennan wastewater plant is required as it is considered a significant cause of mussel decline in the lower reaches of the river.
The species is in serious decline throughout Ireland and Europe and is regarded as one of the world’s most endangered animals.
The Leannan catchment is one of the largest pearl mussel catchments in Ireland. The river flows from Lough Gartan through Lough Fern and through the town of Ramelton into Lough Swilly.
Donegal County Council said that, as a result of the report, Kilmacrennan treatment plant was prioritised for inclusion in the 2010–2012 Water Services Investment Programme.