Which specific US river system harbors the only self-sustaining, year-round freshwater stingray population in North America?

Answer

The St. Johns River system in Northern Florida

The St. Johns River system in Northern Florida is home to the only self-sustaining, year-round freshwater population of elasmobranchs found in North America, consisting of the Atlantic Stingray.

Which specific US river system harbors the only self-sustaining, year-round freshwater stingray population in North America?
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