Great Lakes to Atlantic: The St. Lawrence Seaway System

Ships don't sail "from the Great Lakes to the Atlantic"—they transit a **3,700-km engineered waterway** linking **Lake Superior to the Gulf of St. Lawrence**. The system has three segments.

1. The Great Lakes (Binational)

• Lakes: Superior → Michigan/Huron (connected) → Erie → Ontario
• Control points: **Soo Locks** (Superior→Huron), **Niagara** (bypassed by Welland Canal)
• Depth: 8.2m (27 ft) — **Seawaymax** limit (225.5m × 23.8m × 8.08m)

2. The Welland Canal (Ontario) — The Niagara Bypass

• Length: 43.4 km (27 mi)
• Locks: **8 locks** (Locks 1–7 lift 99.5m; Lock 8 guard)
• Transit: ~11 hours
• Critical: Only link between Erie & Ontario; **bypasses Niagara Falls (99m drop)**
• History: 1st (1829), 2nd (1845), 3rd (1887), 4th (1932 — current)

3. The St. Lawrence Seaway (Montreal → Atlantic) — The International Section

• Length: 306 km (Montreal → Lake Ontario) + **St. Lawrence River to Gulf**
• Locks: **7 locks** (5 Canadian: St. Lambert, Côte Ste. Catherine, Beauharnois x2, Iroquois; 2 US: Eisenhower, Snell)
• Lift: 75m total (Montreal → Lake Ontario)
• Management: **SLSDC (US)** + **SLSMC (Canada)** — binational
• Season: **Late March – Late December** (ice closure)
• Traffic: **40M tonnes/yr** — grain, iron ore, steel, cement, project cargo

Alternative Routes (Historical/Partial)

• Erie Canal (NY): Erie → Hudson → NYC (recreational/small commercial only)
• Oswego Canal: Ontario → Erie Canal (NY)
• Champlain Canal: Champlain → Hudson (NY)
• Chicago Sanitary & Ship Canal: Michigan → Mississippi → Gulf (Asian carp barrier)

Economic Impact

• US$35B+ economic activity annually
• 237,000 jobs (US/Canada)
• Fuel efficiency: 1 laker = 700 trucks = 2.5 unit trains

The Seaway isn't a canal—it's a **binational marine highway**. Without it, the Great Lakes would be a **landlocked sea**.