Three Major Tributaries of the St. Lawrence River in Canada

The St. Lawrence River's Canadian tributaries drain vast areas of the Canadian Shield and St. Lawrence Lowlands. Three major ones:

1. Ottawa River (Outaouais)

• Length: 1,271 km; Basin: 146,000 km².
• Forms ON/QC border; joins St. Lawrence at Montreal (Lac des Deux Montagnes).
• Historic fur-trade route; hydroelectric (Carillon, Chute-à-Blondeau); whitewater rafting.

2. Saguenay River

• Length: 160 km (fjord section); Basin: 88,000 km² (includes Lac Saint-Jean).
• Deep fjord (275 m) carved by glaciers; joins at Tadoussac.
• Whale watching (belugas, blues); Saguenay–St. Lawrence Marine Park.

3. Saint-Maurice River

• Length: 563 km; Basin: 43,000 km².
• Joins at Trois-Rivières (named for its three channels).
• Historic log-driving river; hydro (La Tuque, Shawinigan); Mauricie National Park.

Other notables: Richelieu (Lake Champlain outlet), Manicouagan (hydro giant), Rivière aux Outardes. Together they deliver 60%+ of St. Lawrence flow.