LOL!

You know, this thread started out fairly interesting on kind of a "what if" level, but a 10 second search on Google produces an immediate Aha! response. The Salton Sea, the Great Salt Lake, the Aral Sea, the Dead Sea, California's Pink Lakes – none are used for recreational purposes. The caption to one of the photos of the Pink Lakes says "The red coloration is caused by astronomical numbers of microscopic, unicellular organisms living in the water and salt crust. How they survive the blistering summer heat and concentrated brine is truly remarkable."

I'm sticking with chlorine.