Mattawa River

Mattawa River
Petite Rivière
Pimisi Lake on the Mattawa River.
Name origin: Algonquin language
Country	Canada
State	Ontario
District	Nipissing District
Tributaries
- right	Kaibuskong River Amable du Fond River
Source	Trout Lake
- location	North Bay, Ontario
- elevation	198.5 m (651 ft)
- coordinates	46°18′48″N 79°16′09″W / 46.31333°N 79.26917°W / 46.31333; -79.26917
Mouth	Ottawa River
- location	Mattawa, Ontario
- elevation	148 m (486 ft)
- coordinates	46°19′13″N 78°42′26″W / 46.32028°N 78.70722°W / 46.32028; -78.70722Coordinates: 46°19′13″N 78°42′26″W / 46.32028°N 78.70722°W / 46.32028; -78.70722
Length	76 km (47 mi)
Basin	1,170 km2 (452 sq mi)

The Mattawa River is a river in central Ontario, Canada. It flows east from Trout Lake east of North Bay and enters the Ottawa River at the town of Mattawa. Counting from the head of Trout Lake, it is 76 km in length. The river's name comes from the Algonquin word for "meeting of waterways".

Two provincial parks are located along it: the Mattawa River Waterway Provincial Park stretches along both sides of the river's banks for almost its full length; and Samuel de Champlain Provincial Park, located about 10 km from the river's end.

The river follows inside an ancient fault line through the Algoma Highlands called the Mattawa Fault. This fault line marks the northern edge of an ancient rift valley, called the Ottawa-Bonnechere Graben, and still causes minor earthquakes in the area. From Lake Talon to Mattawa the river flows through a rock-walled canyon up to 150 metres (490 ft) in places.

Tributaries include the:

An interesting feature is the Porte de l'Enfer (Hell's Gate). This is a peculiar cave in the river's bank speculated to be a native ochre mine. As far back as 1761, Alexander Henry the elder reported on this cave and the myths surrounding it. It was said to be inhabited by an evil and fierce demon, hence its name.

Evidence of a post-glacial spillway which drained the Great Lakes into the Ottawa River until about 4000 years ago can be seen at several sites along the river. There are potholes at Portage de Talon and numerous cataracts and former river channels, such as the boulder pavement between Pine Lake and McCool Bay, 12–15 metres (39–49 ft) above the river's present day water-line.