The rivière à Idas (English: Idas River) is a tributary of the north bank of the upper part of the Bras du Nord-Ouest, flowing entirely in the town of Baie-Saint-Paul, in the Charlevoix Regional County Municipality, in the administrative region of Capitale-Nationale, in the province of Quebec, in Canada.

This valley is mainly served by a forest road going up the right bank of the watercourse, as well as by the chemin du rang de Saint-Placide Sud.

The water level of the river varies with the seasons and the precipitation; the spring flood generally occurs in April.

This mouth is located at: From the mouth of the Idas river, the current descends on 14.4 kilometres (8.9 mi) following the course of the Bras du Nord-Ouest; then on 3.2 kilometres (2.0 mi) with a drop of 6 metres (20 ft) following the course of the rivière du Gouffre which flows into Baie-Saint-Paul in the St. Lawrence River.

The toponym “Rivière à Idas” was formalized on March 25, 1997, at the Place Names Bank of the Commission de toponymie du Québec.