It is dammed to form Lake Sainte-Anne, which regulates water supply to the huge hydroelectric plants near the mouth of the Manicouagan and also feeds the Toulnustouc generating station with a capacity of 526 MW, which has been operational since 2005.

It flows, says Mr. C. H. Valiquette, I. C. (1908), in the middle of a valley three quarters of a mile wide composed of land suitable for cultivation.

The north branch, Rivière Toulnustouc Nord, leaves Dechêne Lake about 15 kilometres (9.3 mi) east of the Manicouagan Reservoir.

From there it flows southwest past Lac Fléché and south into the Réservoir Manic 2, which is also fed by the Manicouagan River.

[6] The Toulnustouc River was used for logging by Quebec North Shore Paper (now Produits Forestier Résolu).