Bull Sharks in Freshwater: Risk Level, Behavior, and River Safety Guide
By Sophia Al-Mansoor
Documented encounters span multiple continents. The table below outlines verified upstream migration ranges, typical salinity thresholds, and the primary biological drivers behind inland travel across four major river systems.
| River System / Basin | Max Verified Inland Range | Salinity Profile | Primary Driver |
|---|---|---|---|
| Mississippi River Basin (USA) | Alton, Illinois (~1,750 miles) | 0.0, 0.5 ppt (Pure Freshwater) | Summer baitfish migrations, warm water plumes |
| Amazon River (Brazil / Peru) | Iquitos, Peru (~2,500 miles) | 0.0, 0.2 ppt (Pure Freshwater) | Foraging runs targeting large freshwater teleosts |
| San Juan River / Lake Nicaragua | Full lake transit (~120 miles) | 0.0, 0.1 ppt (Lacustrine) | Year-round nursery residency and breeding loops |
| Brisbane River & Canals (Australia) | Mount Crosby Weir (~40 miles) | 0.5, 15.0 ppt (Brackish to Fresh) | Juvenile nursery habitat, tidal foraging |
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