if you are a diver, then you should visit the cenote Angelita, Mexico. There is a cave. If you dive to depths of 30 meters, the water is fresh water (fresh), but if you dive to depths of more than 60 meters, the water turns salty water, then you can see a "river" at the bottom, complete with trees and foliage leaves. But of course, the river was not unusual, it is a layer of hydrogen sulfide, but it looks like a river ... Wow.
the video ..
http://www.youtube.com/watch?v=VG1FI...layer_embedded