Tristan Island or the Île Tristan is located at the mouth of the Pouldavid Estuary off the French port of Douarnenez in south-western Brittany. It is only about 450 m long and 250 m wide but despite its small size, it has a rich history. It is closely associated with Breton legends and the lost island of Ys. In the Middle Ages a priory was built there and the island was inhabited through much of the 20th century. In the 19th century, it became famous as the site of the first canning factory for sardines fished in the Bay of Douarnenez, the beginning of the sardine industry which was important for this region.
Now uninhabited, the island has become part of the national Parc naturel marin d'Iroise established in 2007. It is accessible to tourists at low tide during spring tides most of the year, for a couple of hours at a time. A schedule is displayed on the mainland just across from the island, or can be obtained from the tourist office. At low tide, the island is connected to the mainland on the Douarnenez side of the estuary.