Upstream of the port, industrial and urban area, the rivière à Mars valley is mainly served by the Consol Paper road.

The rivière à Mars North-West is served by a few other secondary forest roads for forestry and recreational tourism activities.

The mouth of Lac à Mars is located about 11.5 km (7.1 mi) northeast of the boundary of the administrative regions of Saguenay–Lac-Saint-Jean and Capitale-Nationale.

A peninsula attached to the eastern shore stretching on 0.15 km (0.093 mi) in the shape of a hook causes another narrowing in the northern part of the lake.

The toponym "lac à Mars" was formalized on December 5, 1968, by the Commission de toponymie du Québec.