From its source Lake Mégantic in the Estrie region, it runs northwards to flow into the St. Lawrence River opposite Quebec City.

Its principal tributaries are: The river's basin has nearly 50 percent of the faunal richness of Quebec, namely 330 out of 653 vertebrate species known in the province can be found there.

[3] On 6 July 2013 the Lac-Mégantic derailment caused a major oil spill which contaminated the river at its source at Lac Mégantic.

It has shaped its industries and its way of life, particularly in spring when its overflows during snowmelt in inhabited areas are frequent, despite its course regulated by 160 dams and retaining dikes.

The river runs through several towns and villages in the region, including Saint-Ludger, Saint-Gédéon-de-Beauce, Saint-Martin, Saint-Georges, Notre-Dame-des-Pins, Beauceville, Saint-Joseph-de-Beauce, Vallée-Jonction and Sainte-Marie, Quebec.