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Why do young bull sharks enter rivers? Check out this video to learn about why bull sharks choose to leave the ocean and take a swim in fresh water.

Three of the four types of freshwater sharks—the northern river shark, the bull shark, and the speartooth shark—are able to swim in both fresh and salt water. This means that it is especially hard for scientists to track their behaviors, as they are regularly switching between fresh water and salt water. Usually, these sharks spend the majority of their time in salt water, and they swim into freshwater rivers for specific life events, such as giving birth. The Ganges shark is the only shark that must stay in a freshwater environment in order to survive, as it has not adapted to survive in both fresh and salt water. While there are some differences between these four species, there are a few things they have in common. All freshwater sharks have stocky, muscular bodies and tend to be aggressive and unpredictable, especially when provoked. Freshwater sharks tend to have a more fish-like appearance than ocean sharks, making it easy to confuse them with regular river fish. They usually have small eyes and must rely on senses other than their eyesight (such as electroreception) in order to hunt their prey.

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