Although some sharks can swim into river estuaries with mixed fresh and salt water and some even use these areas as a nursery for newborn pups, most of the time they live in salty ocean waters.
However, there are two species of sharks capable of surviving a long time in freshwater with physiological adaptations that allow them to do this.
The bull shark which has been captured in the Amazon River and the Mississippi River several thousand miles far from the ocean and the Bizant River shark which has been caught in Australia in rivers very far from the ocean too.
Although these sharks can survive a long time in freshwater, they do not populate in big numbers freshwater rivers or lakes.
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