St. Lawrence Seaway Flow: Downhill from Lake Superior to the Atlantic

The St. Lawrence Seaway flows downhill (downstream) from the Great Lakes to the Atlantic Ocean.

• Elevation Drop: ~175 m (574 ft) total from Lake Superior (183 m / 600 ft ASL) to sea level.
• Locks: 15 locks (7 Montreal–Lake Ontario, 8 Welland Canal) lift/lower ships to match lake levels.
• Flow Direction: Water flows from Superior → Michigan/Huron → Erie → Ontario → St. Lawrence River → Gulf of St. Lawrence → Atlantic.
• Current: River current aids downstream travel; upstream requires engine power + lockage.

The Seaway is a managed navigation system, not a free-flowing river throughout, but the hydraulic gradient is unequivocally downhill.