The Devon River is a river in the south-west of England. It is formed by the confluence of the rivers DART, Exe and Tamar. The DART is a river in Devon, England that rises in Dartmoor National Park and flows for 70 miles to the sea at Dartmouth. The Exe is a river in Devon, England that rises near Exeter and flows for 60 miles to the sea at Exmouth. The Tamar is a river in Devon, England that rises near Tavistock and flows for 50 miles to the sea at Plymouth.