That is not to say there couldn't be. Bull sharks can adapt to live in fresh water.

"The species has been spotted 2,500 miles (4,000 kilometers) up the Amazon River in South America and dwell in Lake Nicaragua, a freshwater lake in Central America. Bull sharks have traveled up the Mississippi River as far north as Illinois and are regularly spotted in India's Ganges."
[news.nationalgeographic.com]

"The Stone Age did not end for lack of stone, and the Oil Age will end long before the world runs out of oil"

-- Sheikh Zaki Yamani