River Neath (Welsh: Afon Nedd) is a river in south Wales running south west from its source to its confluence with Swansea Bay below Briton Ferry.
It rises in the foothills of the Brecon Beacons with two principal tributaries, the River Hepste and the River Mellte. The River Mellte has a large reservoir constructed in its head-waters, Ystradfellte reservoir.
Although the river starts in the old red Devonian sandstone of south Powys, it soon crosses bands of limestone and millstone grits. In the limestone, it flows partly overground and partly underground through large complexes of caverns, caves and sink holes.
The millstone grit bands create one of the most beautiful series of waterfalls in the UK as the river and its tributaries, including the Afon Pyrddin and Afon Nedd Fechan, descends into the ancient glacial valley of the Neath and onto the Carboniferous coal-measures.
The two main tributaries join about 2 miles north-east of Pont Nedd Fechan to form the River Neath proper which is joined at Pont Nedd Fechan by the Afon Nedd Fechan. The river from this point down is rather linear with few significant tributaries. Those that do join include the Melincwrt Brook and the Clydach brook.
The only major tributary to join is the River Dulais which has its source north of Seven Sisters. As the Dulais nears the Neath it descends a spectacular waterfall: the Dulais falls, a popular tourist attraction and the site of old iron workings.
The River Neath provides water to two canals, the Neath Canal and the Tennant Canal. At Aberdulais basin, both canals meet, the Tennant Canal crossing the River Neath with a fine aqueduct. Also crossing the river here is the Vale of Neath Railway line and the A465 Road.
The estuary of the River Neath extends from Neath town down past Briton Ferry to the sea next to Jersey Marine. The estuary is partly industrialised with a ship breaking yard and a large local authority waste disposal site. Where it remains undisturbed, there are areas of salt marsh of great ecological value.
The River Neath valley once supported many deep coal mines and coal washeries and, in the latter half of the 20th century, some large opencast coal mines. There were also a number of small private drift mines, some of which were using pit ponies until the 1990s.
Near to Resolven a large aluminium plant was established during the war but this ceased working in the 1990s. The main industries in the Neath valley are forestry and farming with most of the population commuting to jobs in Swansea or Port Talbot.