Mattawa Bay is a freshwater body of the southwestern part of the Gouin Reservoir in the territory of the town of La Tuque, in the Mauricie administrative region, in the province of Quebec, in Canada.

This peninsula includes the "Mont de la Tête au Brochet" (English: Mount of the Pike Head) (elevation: 453 metres (1,486 ft)) on the east bank of a strait connecting the northern part of Mattawa Bay with its southern part.

Mattawa Bay is separated from Adolphe-Poisson Bay (located to the west and northwest) by a peninsula advancing northward on 11.7 kilometres (7.3 mi) and an island (length: 5.6 kilometres (3.5 mi)).

Another island (length: 2.2 kilometres (1.4 mi)) straddles the eastern side of the mouth of Mattawa Bay.

From the mouth of Mattawa Bay, the current flows over 116.9 kilometres (72.6 mi) to Gouin Dam, according to the following segments: The toponym "Baie Mattawa" was formalized on December 5, 1968, by the Commission de toponymie du Québec, when it was created.