The freshwater stingrays come from the Amazon river, in South America, as previously stated. As it turns out, the river was recently (geologically speaking) a saltwater river that ran from the Atlantic to the Pacific. However, as the Andes rose, the river's coarse shifted, making it run east, into the Atlantic. Of course this made the river freshwater, but happened very gradually, allowing the marine creatures to adapt. Many neat little creatures stemmed from that change, like the stingrays and the giant piracu.