The Artro enters the sea at a sizeable tidal estuary between Llandanwg and Mochras/Shell Island. The current estuary was formed following a diversion of the Artro by the Earl of Winchilsea in 1819 to improve access to the wharf at Pensarn which was the shipment point for slate from Llanfair and Llanbedr. Prior to this the Artro entered the sea to the south of Mochras.