The high ground forms the catchment area for numerous rivers and streams. There are about of named rivers on Exmoor. The River Exe, after which Exmoor is named, rises at Exe Head near the village of Simonsbath, close to the Bristol Channel coast, but flows more or less directly due south, so that most of its length lies in Devon. It reaches the sea at a substantial ria (estuary) on the south (English Channel) coast of Devon. It has several tributaries which arise on Exmoor. The River Barle runs from northern Exmoor to join the River Exe at Exebridge, Devon. The river and the Barle Valley are both designated as biological Sites of Special Scientific Interest. Another tributary, the River Haddeo, flows from the Wimbleball Lake.