Lake Témiscouata is a lake in the Témiscouata region of southeastern Quebec, Canada. It is 40 km long, with a total area of 66 km. The Madawaska River flows from this lake to the Saint John River.

The cities of Témiscouata-sur-le-Lac, Dégelis and Saint-Juste-du-Lac are located on this lake. Forestry is a major industry in this area.

The Petit Témis Interprovincial Bicycle Path, runs from Rivière-du-Loup, Quebec to Edmundston, New Brunswick, following an abandoned railway line along the lake.

The lake is theorized to be the inspiration for the nearby parish of Saint-Louis-du-Ha! Ha!. One explanation suggests the archaic French word haha, here meaning an unexpected obstacle or abruptly ending path, as the lake is an extremely long and particularly formidable obstacle to travel.