This is my favorite underwater picture so far. It shows a bunch of Simuliidae (black fly) larvae clinging to a rock and swinging in the fast current. There are also at least four visible mayfly nymphs, probably in the family Baetidae.
In this picture: True Fly Family Simuliidae (Black Flies) and Mayfly Family Baetidae (Blue-Winged Olives).
Troutnut.com is a collection of pictures and information about fly fishing. Fly fishermen, fly tiers, and trout enthusiasts of all stripes can learn more about life beneath the surface of trout streams, as well as how to better imitate aquatic insects with artificial flies to catch trout. There are aquatic insect pictures, underwater pictures, landscape pictures, and a comprehensive reference to the common names of trout stream insects.