The Avill rises on the eastern slopes of Dunkery Beacon, the highest point on Exmoor. It flows in an easterly direction to Steart where it is joined by streams from White Moor and Kersham Hill . It then turns north for a short distance to Pitt Bridge and then north easterly past Timberscombe. It then flows through the valley below Knowle Hill and through Dunster to the sea at Dunster Beach, into the Bristol Channel.
At Loxhole Bridge, Dunster a sluice controlled overflow channel has been constructed to take water from the river into the Bristol Channel just east of the river’s mouth.