River Neath (Welsh: Afon Nedd) is a river in south Wales running south west from the point at which its headwaters arising in the Brecon Beacons National Park converge to its mouth at Baglan Bay below Briton Ferry on the east side of Swansea Bay.

The rivers Nedd Fechan, Mellte and Hepste rise in south Powys on the southern slopes of Fforest Fawr.

Each then crosses a band of Carboniferous Limestone before traversing country formed by interlayered sandstones and shales traditionally referred to as the Millstone Grit.

As the Dulais nears the Neath it descends the Aberdulais Falls, a popular tourist attraction owned and managed by the National Trust and the site of an old tinworks.

The estuary is partly industrialised with a ship breaking yard, a large local authority waste disposal site and wharves at Melincryddan, Briton Ferry and Neath Abbey.

Where it remains undisturbed, there are areas of salt marsh stretching from Neath to Baglan Bay and Crymlyn Burrows which are of great ecological value.