Check out this picture snapped by Astronaut Scott Kelly from the International Space Station. He tweeted the picture early on May 7th, and it looks like the river is floating!
The river is the Bighorn River, which flows through Wyoming and Montana. The 'floating' is actually an optical illusion.
According to Attila Nagy of Gizmodo this illusion is known as a "relief inversion, and you may often experience it when looking at satellite photos taken in such a way that the Sun illuminates the landscape from below. This jars with our common (unconscious) expectation derived from everyday experience of the Sun shining on objects from above. Our brain finds it hard to interpret the sight."
But if you rotate the picture 180°, the optical illusion is foiled. The river appears now to be flowing normally through a canyon.