Although some sharks can swim into river estuaries with mixed fresh and salt water and some even use this areas as
nursery for young sharks, most of the time they live in ocean water.
However there are two species that are capable of surviving long time in fresh water with physiological adaptations
that allow this.
The bull shark which have been captured in the Amazon river or the Mississippi river several thousand miles far
from the ocean and the speartooth shark which has been captured in Australia in rivers very far from the ocean
too.
Though these sharks can survive long time in fresh water, there are no populations developing in fresh water rivers
or lakes.