The surface of the Saint-Cyr South River is usually frozen from early November to mid-May, however, safe ice circulation is generally from mid-November to mid-April.

The Saint-Cyr River South originates at the mouth of Barry Lake (Saint-Cyr River South) (length: 12.9 kilometres (8.0 mi); elevation: 392 metres (1,286 ft)) which straddles the townships of Barry and de Bailly, in Senneterre; in addition, a bay advances towards the North over a hundred meters in the township of urban, as well as the bay leading to the mouth of the lake.

It sneaks northward forming the lakes Bailly, Barry and Saint-Cyr then flows into the Opawica River through Doda Lake. "

In return, the hydronym "Rivière Saint-Cyr" remains the name of the segment of 48.9 kilometres (30.4 mi) of the northern part (slope of the Nottaway River) in Nord-du-Québec.

Shortly thereafter, Arthur Saint-Cyr became responsible for the location and construction of the Quebec Central Railway to connect the cities of Lévis and Sherbrooke.