The River Otter rises in the Blackdown Hills just inside the county of Somerset, England near Otterford, then flows south for some 32 km through East Devon to the English Channel at the western end of Lyme Bay, part of the Jurassic Coast, a UNESCO World Heritage Site. The Permian and Triassic sandstone aquifer in the Otter Valley is one of Devon's largest groundwater sources, supplying drinking water to 200,000 people.