The Three Sisters (Irish: An Triúr Deirfiúr) are three rivers in Ireland: the River Barrow, the River Nore and the River Suir. The Suir and Nore rise in the same mountainous area in County Tipperary, near the Devil's Bit, while the Barrow rises in the Slieve Bloom Mountains in County Laois. The Nore flows into the Barrow about 17 km before the Suir and Barrow join to form an estuary called Waterford Harbour east of the city of Waterford. The rivers fan out to drain a large portion of the southern part of the island, including Counties Tipperary, Carlow, Kilkenny, Wexford and Waterford, among others.
The lengths of the three rivers of the Three Sisters are the Barrow - 192 km (119 mi), the Suir - 185 km (115 mi) and the Nore - 140 km (87 mi).
The combined catchment area of the Three Sisters is 9,207 km2, made up of the Suir's (3,610 km2), the Barrow's (3,067 km2) and the Nore's (2,530 km2).[1]
The combined long term average flow rate of the Three Sisters into Waterford Harbour is 157 m3/s, almost half of which is made up of the Suir's (76.9 m3/s), followed by the Nore's (42.9 m3/s) and the Barrow's (37.4 m3/s).[1]
The Barrow Bridge crosses two of the Three Sisters, the Nore and the Barrow. They then join the River Suir just downstream of the bridge. This place is known in Irish as Cumar na dTrí Uisce, "the confluence of the three waters". The Nore joins the Barrow some four kilometres north of New Ross and the combined waters of the three sisters that can be seen from Cheekpoint. The combined waters of all three sisters are then visible all the way down the estuary from Cheekpoint on.
In ancient times, the area bounded by the Suir and the Barrow formed the Kingdom of Ossory. This name is retained today for dioceses in both the Roman Catholic Church and the Church of Ireland.