Back eddies on rivers, small streams, and creeks offer wild trout the perfect habitat by providing a steady stream of food, protection from predators, and retreat from heavy currents. My colleagues and I like to refer to such areas as "Merry Go Rounds", because of the circulating movement they possess. Natural foam is the key ingredient here, emerging insects, adults, and spent spinners, along with terrestrials get caught up in the foam and are trapped. As the smorgasbord of food revolves overhead of a wary trout, it can take its time and selectively feed. Often while watching Merry Go Rounds, slight dimples, and snouts can be detected within the surface film. The other advantage to the trout is the foam acts like a safety barrier, and because of such they feel more secure. Think of a Dorado hovering below a kelp patty in the Pacific Ocean.
Whether I'm guiding or fishing on my own, I always keep an eye out for back eddies, or areas with foam lines. "Foam is home" couldn't be truer words spoken.