|Ewenny River (Afon Ewenni)|
The river at Ewenny, the village to which it gave its name.
|Countries||United Kingdom, Wales|
|County||Vale of Glamorgan|
|- left||Afon Alun, Afon Ewenni Fach, Nant Canna, Nant Crymlyn|
|Cities||Pencoed, Ewenny, Ogmore|
|- location||North of Pencoed, Bridgend County Borough, Bridgend, Wales|
|Length||11.0 km (7 mi)|
The Ewenny River (Welsh: Afon Ewenni) is a small river in south Wales with a length of ten miles or sixteen kilometres. For most of its length it forms the border between the counties of the Vale of Glamorgan and Bridgend. It is a major tributary of the River Ogmore, which it joins over a mile upstream from the sea at Ogmore Castle. It is a popular river amongst anglers.
The river rises to the north east of Bridgend town, in South Wales, where two minor rivers known as Ewenny Fach (Little Ewenny) and Ewenny Fawr (Big Ewenny) join. Ewenny Fach is considered a tributary of the Ewenny Fawr, which in turn is formed when three streams, Nant Canna, Nant Ciwc and Nant Crymlyn join. 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, which rather damages the water quality. The river flows through the villages of Ewenny and Ogmore, before entering the River Ogmore estuary just below Ogmore Castle. One of its main tributaries is the Afon Alun, which flows west for a few miles, and converges with the Ewenny north of Ogmore.
Historically, the river meandered among moors and wetlands, frequently flooding, but with wide biodiversity. Being south of the South Wales coalfield, no mining-related industrialisation and pollution affected the river. However, in the 20th century, despite being away from urban areas, industrial plants sprung up along the river. During the early 1970s a long stretch of meandering river through lowland meadows was canalised and lined with vertical steel piles in order to protect the developing site of the Ford engine plant from flooding. Unfortunately, these diversion projects degraded the river slightly. On October 22, 2010, 20,000 litres of diesel escaped into the river. After a cleanup effort, the Environment Agency found the source of the leak. 
The river joins the Ogmore near Ogmore Castle, which is south of the river. At the confluence, a series of stepping stones cross the river. However, these only cross the Ewenny river, and not the Ogmore. There is no sufficient way to cross the rivers from the northern bank; a bridge to the Penybont works is inaccessible, and the next bridge is many miles upstream. Dangerous currents make the river difficult to wade over. The lower portions of the Ewenny and Ogmore are tidal; the stepping stones are submerged at most tides. The tides and rivers are extremely fast flowing and deep in places; undercurrents are documented, as is a rip current.