The Mégiscane River rises at the mouth of Lac Françoise (length: 1.3 kilometres (0.81 mi); elevation: 434 metres (1,424 ft)).

The toponym "Mégiscane River" was formalized on December 5, 1968, at the Commission de toponymie du Québec.

After several hesitations, the Government of Quebec authorizes the partial diversion of the Mégiscane to the Saint-Maurice River basin in 1951.

This project was carried out in parallel with the installation of additional turbines at the Rapide-Blanc, Trenche and La Tuque.

The total cost of the project, which has increased the company's installed capacity of 150,000 horsepower (110,000 kW) (120 megawatts (160,000 hp)), is estimated to $14 million.