This isn't really an underwater picture, but a picture taken into my aquarium of midge larvae which lived in the silt I used for substrate. Each larva has a little tower of detritus (Detritus: Small, loose pieces of decaying organic matter underwater.) built up along the bottom, while the bare larva waves around from the top.
In this picture: True Fly Family Chironomidae (Midges).
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.