Lakes and rivers are easy to picture as murky and lifeless. Below the surface, it’s another world entirely: forests of aquatic plants bathed in green light, sunken tree stumps where predators lie in wait, and encounters that rival anything in the ocean. The wels catfish, a placid giant that can grow longer than six and a half feet (2 m), glides out of the shadows trailing its long barbels; the zander, its eyes built for the gloom, waits motionless among the stems. On scuba or on a single breath, freshwater photography takes patience and a light touch: here, good visibility has to be earned, and every image is won just a few yards from shore.