The Afon Mellte is a river in the Brecon Beacons National Park, flowing through the area known as Waterfall Country, north of Pontneddfechan in Powys, South Wales. It is notable for its dramatic gorge sections, multiple large waterfalls, and a cave system that directly shapes the paddling experience.

The classic paddling trip on the Mellte puts in where the river emerges from Porth yr Ogof Cave, making for a distinctive and unusual start to a run. From there, easy Grade 3 rapids characterize the upper section. The trip is described as involving as much walking as paddling, which paddlers should factor into their planning and time estimates.

The river's upper section, north of the confluence with the Afon Hepste, features three large waterfalls and a cave — significant hazards that require portaging and careful navigation. The lower 2 miles of the Mellte, south of the Hepste confluence, are less frequented and have fewer marked paths along the banks, which has implications for self-rescue and egress options.

A practical access point is at Dinas Rock (Craig y Ddinas), a former quarry site at the confluence of the Mellte and the Afon Sychryd. Parking is available at no charge, though it can fill up during busy periods and is locked at dusk, which limits late takeouts and rules out overnight stays. The Sgwd yr Eia Trail and the Four Waterfalls Loop are popular walking routes in the area, meaning the riverside paths can see significant foot traffic.

The lower Mellte passes through the site of the Glyn Neath Mills, a former gunpowder works established in 1857 and closed in 1931, where numerous industrial ruins remain spread over approximately 1.6 miles along the north bank. The river eventually meets the River Neath near Pontneddfechan.

The river runs through a gorge environment with confined sections, and water levels are a key consideration — video footage references a gauge reading of just over 1 metre as a prime level for whitewater kayaking, suggesting the river is level-dependent and best paddled after rainfall.