 Most other rivers arising on Exmoor flow north to the Bristol Channel . These include the River Heddon , which runs along the western edges of Exmoor , reaching the North Devon coast at Heddon 's Mouth , and the East and West Lyn rivers , which meet at Lynmouth . Hoar Oak Water is a moorland tributary of the East Lyn River , the confluence being at Watersmeet . The River Horner , which is also known as Horner Water , rises near Luccombe and flows into Porlock Bay near Hurlstone Point . The main exception to northward @-@ draining rivers is the River Mole , which arises on the south @-@ western flanks of Exmoor . It is the major tributary of the River Taw , which itself flows northward from Dartmoor . Badgworthy Water is one of the small rivers running north to the coast and is associated with the Lorna Doone legends . 
