I took this photo during a boat ride on the Colorado River. I liked the way the canyon walls reflected in the water near the boat's wake. Since the water was crystal clear, why do you see the reflection of the canyon, instead of seeing through to the bottom of the river?
The clue is the shadows on the cliff. While the sun was shining directly on the water, quite a bit of light was penetrating the water, and we could see fish swimming along the bottom. Once the sun set enough for the river to be in shadow, the water became much more mirror-like. You can see something similar with the windows of your house. During the day, you can see out your windows easily, but if it is dark outside, you mostly see your own reflection.