The Nenagh River (Irish: An Ghaothach) rises in the Silvermine Mountains in County Tipperary, Ireland. It flows east of Nenagh and into Lough Derg just north of Dromineer.
The river, and its tributary the Ollatrim river, is popular for angling, it holds a stock of wild salmon and trout. There are also coarse fish particularly near the mouth of the river during spawning times. Funds were allocated to the Ormonde Anglers Association to improve areas for spawning and in-stream structures improving access, fencing, protecting banks and installing a number of deflectors. There is 22 km of trout fishing and a further 15 km on the Ollatrim. It is classified as a rich lowland river.
Slí Eala ("Way of the Swan") is a 10 km waymarked trail which follows the banks of the Nenagh River from Dromineer via Ballyartella to Scott's Bridge, on the N52 road north of Nenagh. The walk takes its name from the population of mute swans on the river. There are trailheads at Scott's Bridge and in Dromineer village.
There are several bridges over the river.
Ballynaclogh bridge, built in about 1700, four arched limestone bridge with refuges for pedestrians. Widened in about 1750.
Tyone Bridge (c. 1830) with three limestone arches carries the R498 road over the river just south of Nenagh town.
Bennett's Bridge is a modern bridge carrying the R445 road, (previously the main Dublin to Limerick road) over the river at Lisbunny.