The source of the Plym is on Dartmoor, some 1500 feet above sea level, in a marshy area lying between Crane Hill and Great Gnat’s Head known as Plym Head. It flows approximately south-west for 18 miles before reaching the sea at Plymouth Sound. The sound and the adjacent city of Plymouth taking its name from the river. Five miles from its source the Plym is joined by the Blacka Brook. From this point to Cadover Bridge it meanders through an almost flat area of alluvium and rock debris, the legacy of centuries of tin mining and china clay working. At Shaugh Bridge the River Meavy joins the Plym from the north. The River Meavy source at Meavy Head on the outskirts of Princetown and the river's route has included a spell in Burrator Reservoir.