The River Horner, also known as Horner Water, rises near Luccombe on Exmoor, Somerset, and flows past Porlock into Porlock Bay near Hurlstone Point on the Bristol Channel. The river flows into the sea though a shingle ridge at Bossington beach, where it forms part of the Porlock Ridge and Saltmarsh Site of Special Scientific Interest. When the river level is very high, flood water builds up behind the ridge, causing it to breach.