When I visited the Great Smoky Mountains a couple of weeks ago, fall foliage was not at its peak and there were few red leaves in the park. One afternoon, we experimented with using a polarizing filter to remove reflections from water, so that the water surface disappeared. One of the few red leaves I saw that day was submerged in several inches of water at the edge of a stream. The leaf was barely visible at first because the sky reflecting on the water’s surface obscured it. Using a polarizer to remove the reflection caused the red leaf to suddenly “pop” and become visible despite being submerged.