| Saint-Cyr | |
| Map: | Nottaway map.png |
| Subdivision Type1: | Country |
| Subdivision Name1: | Canada |
| Subdivision Type2: | Province |
| Subdivision Name2: | Quebec |
| Subdivision Type3: | Region |
| Subdivision Name3: | Nord-du-Québec |
| Length: | 48.9km (30.4miles)[1] |
| Source1: | Barry Lake (Saint-Cyr River South) |
| Source1 Location: | Eeyou Istchee James Bay (municipality), Nord-du-Québec, Quebec |
| Source1 Coordinates: | 49.0086°N -75.5731°W |
| Source1 Elevation: | 395m (1,296feet) |
| Mouth: | Mégiscane River |
| Mouth Location: | Eeyou Istchee James Bay (municipality), Nord-du-Québec, Quebec |
| Mouth Coordinates: | 49.32°N -75.3117°W |
| Mouth Elevation: | 338m (1,109feet) |
| Tributaries Right: | Doda Lake |
The Saint-Cyr River is a tributary of Doda Lake, flowing into the municipality of Eeyou Istchee Baie-James (municipality), in Jamésie, in the area of Nord-du-Québec, Quebec, Canada.
The Saint-Cyr river flows successively into the townships of Urban, Lacroix, Belmont and Royal. Forestry is the main economic activity of the sector; recreational tourism activities, second.
The Saint-Cyr River valley is served by the forest road R1053 (east-west direction) which passes on the north-west side and north of Lac Saint-Cyr. This road joins the road R1009 (North-South direction) which passes to the East of the Aigle River (Doda Lake).
The surface of the Saint-Cyr River is usually frozen from early November to mid-May, however, safe ice circulation is generally from mid-November to mid-April.