Bryozoans
Even the clearest water has at least some particles suspended in it -- sand, silt, plankton, who knows what -- and most of the time, in most places, the water isn't really all that clear. In fact, during a plankton bloom or after a storm that has caused a lot of runoff, you might just as well leave your camera on the boat. Light from a camera strobe has a nasty habit of bouncing back from any particulate matter that it encounters between the camera lens and the subject. The result is the bane of underwater photography: backscatter. Your images will look as though they were taken in a…