The Lake Guerlédan is the largest Brittany Lake (400ha).The dam Guerlédan was built between 1923 and 1925 in the sinuous throats of Blavet.The lake is 12 km long . The Lake Guerlédan is fed by the Channel from Nantes in Brest.
The lake finishes in the West on the level of the lock of Bellevue.
A river licence is obligatory on the lake for the boats with engine of more than 10cv. The boats must be registered into maritime or river.
