The River Nore ( ) is one of the principal rivers (along with the River Suir and River Barrow) in the South-East Region of Ireland. The river drains approximately of Leinster and Munster, that encompasses parts of three counties (Tipperary, Laois, Kilkenny). Along with the River Suir and River Barrow, it is one of the constituent rivers of the group known as the Three Sisters. Starting in the Devil's Bit Mountain, County Tipperary, the river flows generally southeast, and then south, before its confluence with the River Barrow at Ringwood, and the Barrow railway bridge at Drumdowney, County Kilkenny, which empties into the Celtic Sea at Waterford Harbour, Waterford. The long term average flow rate of the River Nore is 42.9 cubic metres per second (m3/s) The river is home to the only known extant population of the critically endangered Nore freshwater pearl mussel, and much of its length is listed as a Special Area of Conservation. Name The river is known in Irish as An Fheoir. The River Nore was mentioned in the Martyrology of Oengus the Culdee (Félire Óengusso Céli Dé), published before 824. He spoke, in Old Irish, of or "the cold-pure Nore." A Middle Irish reference, from before 1420, refers to "The fair wide plain of the Feoir" (Fiond-chlár fairsing na Feoire). The name is believed to derive from Irish "green bank, edge or shore of sea, lake or river"; the Old Irish means "green bank or shoreland." Course The Nore rises on the eastern slopes of the Devil's Bit Mountain in the townland of Borrisnoe, County Tipperary. It then flows south-eastwards to County Laois and County Kilkenny before joining the River Barrow just north of New Ross near the Barrow Bridge. The river passes near Durrow, County Laois then through Ballyragget, the city of Kilkenny and then the villages of Bennettsbridge and Thomastown. Further south, it forms a picturesque V-shaped river valley, particularly notable near the village of Inistioge, the tidal limit. Major tributaries of the Nore include the Dinan, the Breagagh at Kilkenny City, the King's River, the Little Arrigle and the Black Water. List of places along the river. Devil's Bit Mountain (begins) Castletown Durrow, County Laois (near) Ballyragget Kilkenny Bennettsbridge Thomastown Inistioge List of tributaries River Erkina River Dinan (Dinin, Deen) White Horse (Mountrath River) Breagagh King's River Little Arrigle Black Water Geology and morphology The Nore rises on a sandstone base