A Canvasback dives up to 30 ft. underwater to get roots, buds, and tubers of aquatic plants. Also eats aquatic insects, small fish and crustaceans. This particular duck was diving in very cold and pretty shallow water on an overcast day. And it wasn't until I saw the image later that I reallized how a shallow muddy bottom can apply a mud pack to the poor duck's face. The Canvasback second from the left was just starting it's search for food a few days later when the sun was out. Note the clean face. The image third from the left shows that same duck after a couple of shallow dives to the mud in San Francisco Bay...