Thanks, Ravikiran, Danir and Mohain,
The 'reflected' color in the first is a combination of sky reflection and the sand at the bottom of the river. The water is about a foot deep and very clear at this point.
The second shot is what happens when water 'sheets' over a large surface of sand. Saturation occurs, currents develop, and braiding, or interweaving takes place. The water is about 4 inches deep toward the top of the photo (where the current is strongest) and only about 1 inch deep at the bottom (where the water slows and begins "sheeting"). This slight channeling will change every couple hours or so.
The river flows mainly underground at this point, so as the weather warms and the flow sinks back into the sand, this is a very likely place for quicksand to develop.