The Blavet (French pronunciation: [blavɛ]; Breton: Blavezh) river flows from central Brittany and enters the Atlantic Ocean on the south coast near Lorient.

From the last lock at Polvern, the river is tidal and considered as a maritime waterway, giving access to the seaport of Lorient and the Atlantic Ocean.

Today, boats coming from Nantes via Redon have to take the Canal du Blavet in order to reach the ocean near Lorient.

Like the entire Brittany canal network, its raison d’être was military defence in case of a naval blockade of the coast by the British Navy.

[2] The waterway has little recreational traffic because of the large number of locks in the watershed section of the Nantes-Brest canal between Pontivy and Rohan, and the effective barrier of Guerlédan Dam to the west.