For most of its 10 miles (16 km) length, it forms the border between the Vale of Glamorgan and Bridgend.

This branch of the river flows southeast, past the village of Pencoed and under the M4 Motorway until it is joined by the Ewenny Fach south of Junction 35 of the road .

From here, the river turns southward and flows through the Ewenni Moor, past the village of Waterton.

Waterton is the site of a large industrial estate, and a few miles of meandering river were straightened and diverted to prevent flooding.

[1] One of its main tributaries is the Afon Alun, which flows west for a few miles, and converges with the Ewenny north of Ogmore.