Milford Haven Waterway is a natural harbour in Pembrokeshire, Wales. It is a ria or drowned valley which was flooded at the end of the last ice age. The Daugleddau estuary winds west to the sea. As one of the deepest natural harbours in the world, it is a busy shipping channel, trafficked by ferries from Pembroke Dock to Ireland, oil tankers and pleasure craft. Admiral Horatio Nelson, visiting the haven with the Hamiltons, described it as the next best natural harbour to Trincomalee in Ceylon and "the finest port in Christendom". Much of the coastline of the Waterway is designated as a Site of Special Scientific Interest, listed as Milford Haven Waterway SSSI.