Green Bay (Lake Michigan): Dimensions of the World's Largest Freshwater Estuary
Green Bay: By the Numbers
Green Bay is a massive arm of Lake Michigan, extending deep into Wisconsin's coastline. It holds the distinction of being the world's largest freshwater estuary—where the Fox River meets the lake, creating a nutrient-rich mixing zone.
Key Statistics
| Metric | Value |
|---|
| Length | 118 miles (190 km) |
| Maximum Width | 50 miles (80 km) |
| Surface Area | 2,044 sq mi (5,295 km²) |
| Average Depth | ~30 ft (9 m) |
| Max Depth | ~100 ft (30 m) near the mouth |
| Watershed Area | 15,000+ sq mi (draining 40% of WI land area) |
Ecological Significance
- Estuary Dynamics: Warm, nutrient-rich Fox River water overlays colder lake water → high productivity → supports massive walleye, yellow perch, whitefish, and migratory bird populations.
- Wetlands: 16,000+ acres of coastal wetlands (Cat Island Chain restoration project).
- Dead Zone: Summer hypoxia (low oxygen) in lower bay from agricultural runoff—major focus of EPA/WDNR cleanup (Fox River PCB remediation, TMDL for phosphorus).
Human Use
- Port of Green Bay: 2M+ tons/year (coal, limestone, salt, cement, forest products).
- Recreation: Fishing (walleye capital), boating, waterfowl hunting.
- Cities: Green Bay (107k), Marinette (10k), Sturgeon Bay (9k), Escanaba, MI (12k).
Geologically young (~10,000 years post-glacial), Green Bay is a working waterway, an ecological engine, and a recreation playground—all in one.
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