This phenomenon stems from the little slope on the course of the river, between "lac à la digue" to its mouth in the Rivière du Milieu (Mékinac).

The name "Rivière aux eaux mortes (Mékinac)" was officially registered on December 5, 1968 in the Bank of place names of the Commission de toponymie du Québec (Geographical Names Board of Québec)[1] The "Rivière aux eaux mortes (Mékinac)" takes its source from several lakes in the high mountains of the Portneuf Wildlife Reserve: "lac à l'Orignal" (moose lake), Desrochers, Turner, Aumond, Liserons, Pilote, "aux oreilles" (ears), "du Mâle" and "du coin" (corner).

From that junction, the river flows South-West on 3.6 km up to the mouth of "Lac à l'Ours" (Bear Lake).

In summary, the river flows on 33 km (measured by water) from Lake Dussault dam down to its mouth.

Observational nature enthusiasts will love the range of concentration of waterfowl, located in a wetland on the "Rivière aux eaux mortes".