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.
Some large Ephemerella mayfly nymphs cling to a log. In the background, hundreds of Simuliidae black fly larvae swing in large clusters in the current.