The Chenal du Four is a waterway off the coast of Brittany in north-western France, in the area of Porspoder, between Pointe Saint-Mathieu and the . It is marked by six lighthouses including the Saint-Mathieu Lighthouse and the . The passage maintains a depth of at least 25 feet (7.6 m) at low tide, and is the usual path taken by yachts sailing between the English Channel with the western coast of France.