The lake, which was originally called the Yeo reservoir, covers . The River Yeo rises in the centre of Compton Martin village, from there it flows past the village of Ubley and enters Blagdon Lake. From the lake the river flows south of Wrington and Iwood, where there were once a series of watermills along its banks. Its route then takes it around the northern outskirts of Congresbury, and across the North Somerset Levels roughly parallel to the A370 road, past the site of a Roman villa before crossing under the M5 motorway and emptying into the Severn Estuary in Woodspring Bay, downstream from Clevedon and west of the village of Kingston Seymour. The watershed catchment area of the reservoir is .