Some sharks like freshwater, too (VIDEO)

WASHINGTON – Don’t get too comfortable swimming in that cool, refreshing river. It might not be the ocean, but that doesn’t mean sharks aren’t lurking beneath the surface.

The toothy predators can be found in placid lakes, estuaries, large streams and rivers when the climate is warm, temperate or tropical, says Discovery.

One of the biggest hot spots for freshwater sharks in the U.S. is the Mississippi River. They have also been confirmed as far north as Illinois.

In South America, bull sharks were once so common in Lake Nicaragua that researchers thought that is where they originated. Locals prized their fins, and the Nicaraguan government eventually imposed a ban on shark fishing in 2006.

Watch a video of the creatures below:

Usually found in salt water, these predators survive salinity changes by giving their kidneys a workout. They take in extra water and urinate more than 20 times as often as when they are in salty water, experts say.

So next time you decide to tube down the river, make sure to keep an eye out.

WTOP’s Kristi King contributed to this report. Follow Kristi King and

(Copyright 2012 by WTOP. All Rights Reserved.)

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