The Pessamit Innu, called Riverin by the Europeans, hunted and fished by the river until around 1900. The name of the river, which dates back to at least 1913, reflects the presence of these people in the area.
River
The Riverin River has a length of and a vertical drop of. The mean flow varies from, with an annual average of. The Simard Fall is from the river mouth and the Fred Fall is from the mouth. There is a dam at a distance of from the mouth. Below the dam there is a high cascade. An unnamed fall from the mouth prevents saltwater tides from flowing further upstream. The Riverin River is not recognized as a salmon river. There are rainbow smelt at the mouth of the river, and other fish include American eel, brook trout and three-spined stickleback.
Dam
The high Barrage de la Rivière-Riverin retains a head of and holds in a reservoir. The dam was built in 1946. It is a concrete structure long on a rock foundation. The present 2.01 MW power plant is owned by Pouvoir Riverin and Algonquin Power Fund and came into operation in 1999.
Watershed
The Riverin watershed covers, equally divided between the unorganized territory of Lac-Walker and the town of Port-Cartier. To the east the watershed is bordered by the watershed of the Pentecôte River, and to the north and west by the watershed of the Aux Rochers. The watershed is about long from north to south, and about wide inland, shrinking to less than wide in the coastal plain. The coastal plain extends inland for about, gradually rising to an elevation of. Beyond this the river basin is in a rocky plateau with rounded hills, sometimes with steep slopes. The highest point is in the northeast of the watershed. The land is based on magmatic rocks, including assemblages of anorthosite and gabbro-norite, syenite, monzonite, granodiorite and diorite, migmatite, granite and pegmatite. In the plateau the bedrock is often exposed in outcroppings, or is covered with a thin layer of soil. The coastal plain has large amounts of clay and silt sediments deposited by the Goldthwait Sea after the glaciers withdrew, which were then covered by coarser sandy estuarine and deltaic sediments. Wetlands account for 5.63% of the basin, and are found on the coastal plain in flat areas with fine sediments. Upstream, the rivers follow angular courses dictated by fractures in the bedrock. In the coastal plain the rivers develop meanders in the loose sediments.
