The Cadoxton River is one of the smaller rivers in South Wales, and has been extensively modified in the past as the area has developed and become urbanized. The source lies to the north of Dinas Powis, where the Wrinstone Brook joins Bullcroft Brook, and just upstream of this confluence, there are a series of weirs and basins known as salmon leaps which are used for trout farming. The river in this area is very rural, running through the valley of Michaelston-le-Pit, hidden away from the surrounding urban areas of Caerau, Llandough and Dinas Powis.
From this pastoral valley, the river flows past the remains of the castle, and into Dinas Powis. It runs under the main road near to the village centre, before cutting round behind the railway line, picking up the main road to Barry on the outskirts. Leaving Dinas Powis behind, the river flows across the barren Cog Moors alongside the A4055, all the way to the Biglis Roundabout, where Sully Moors road and the A4231 Docks Link meet.
Originally, the river took the route of what is now Cardiff Road to the sea, but in the late 19 th century, it was diverted in order to allow Barry Docks to be constructed. The river mouth was reconstructed to become the dock entrance and locks, and the river bed dug out to become number one dock. The river was diverted into a channel which runs in straight lines down between the chemical works to a new river mouth cut into the stone near Bendrick Rock. This stretch of the river should be tidal, but a dam and flap valve constructed at the same time as the docks keeps salt water out of the river.
The lower reaches of the Cadoxton were heavily polluted by chemical effluents from the 1940s through to the 1970s, but environmental regulation and voluntary improvements by the chemical companies mean that the river now meets good quality standards, and supports fish, including escapees from the trout farm.
The old course of the river is still visible in places, notably the ponds and reed beds on the land adjacent to Dow Corning, which is now a nature reserve and angling centre for the Glamorgan Anglers.
