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.

For the river in Devon, England, see River Otter

River otter refers to several species of aquatic mustelids within the genera Lutra, Lontra and Pteronura, which mainly inhabit rivers and other freshwater locations. This distinguishes them from the sea otter and marine otter which are true marine mammals.