St. Lawrence River & Lake Ontario: Flow Direction Clarified

Correction: The St. Lawrence River flows out of Lake Ontario, not into it.

The Hydrologic Sequence

The Great Lakes form a west-to-east staircase:

1. Lake Superior (183 m) → St. Marys River →
2. Lake Michigan-Huron (176 m) → St. Clair/Detroit Rivers →
3. Lake Erie (174 m) → Niagara River (Niagara Falls) →
4. Lake Ontario (75 m) → St. Lawrence River → Gulf of St. Lawrence → Atlantic

St. Lawrence River Key Facts

• Length: 1,197 km (744 mi) from Lake Ontario to Gulf
• Drainage: 1.34M km² (includes all Great Lakes)
• Flow: ~10,000 m³/s average at Québec City
• Sections: Lake Ontario → Thousand Islands → Lake St. Lawrence (reservoir) → Montréal (head of navigation) → Fluvial estuary → Maritime estuary → Gulf

Why the Confusion?

Rivers usually flow into lakes. But Lake Ontario is the outlet for the entire Great Lakes system. The St. Lawrence is the drainage river.

Human Engineering

• Moses-Saunders Dam (1958): Creates Lake St. Lawrence; enables seaway navigation + hydropower.
• St. Lawrence Seaway: 15 locks lift ships 168 m from Montréal to Lake Erie.
• Water level regulation: Plan 2014 balances hydropower, shipping, wetlands, erosion.

Ecological Significance

The river hosts endangered species (lake sturgeon, American eel), critical wetlands (Lake St. Pierre RAMSAR site), and is a migratory corridor for Atlantic salmon (reintroduction efforts).