I'll keep it in mind, and let my friends check the water first.

I used to swim just about anywhere, in freshwater or salt, but I've heard so many shocking tales of water beasties I've become more cautious. In the last few years I've learned of bull sharks (also called Zambezi sharks) that swim everywhere that people do--in salt, brackish, and freshwater, thousands of miles up rivers, and eat people.   "Bull sharks have been found thousands of miles up the Amazon River, and in Nicaragua have been seen leaping up river rapids, salmon-like, to reach inland Lake Nicaragua." http://animals.nationalgeographic.com/animals/fish/bull-shark.html   Images: http://www.christinacjones.com/wp-content/uploads/2007/06/bull-shark.jpg http://www.sharkdiving.us/images/bull/07.jpg   "Bull sharks (Carcharhinus leucas) are found in tropical and subtropical waters almost everywhere in the world, whereby they prefer to live close to, or even in rivers. They belong to a minority species, capable of living in sweet water as sexually mature individuals. They are thus found in various rivers such as the Mississippi, the Amazon or the Zambezi. In the Mississipi river they are found all the way up to Illinois, and in the Amazon as far inland as 3,500 km. But whole populations, not just single individuals, also live in such sweet water lakes as Lake Nicaragua or Lake Isabel in Guatemala. Their capability of tolerating varying saltwater levels means they can also be found in brackish water systems, like the Indian River System near Cape Canaveral (Florida). Bull sharks often live so long in sweet water that their metabolism adjusts to the missing salt. ... "Bull sharks may grow to a length of 350 cm and weigh about 230 kg." http://sharkcentral.blogspot.com/2009/07/bull-shark.html