Wild One,

Google Chironomidae and you will find plenty of pictures of larvae, pupae and adults. One of the best sites is The Chironomid Home Page although it is a site for chironomid biologists and can get a bit techical. There are many species of chironomids ranging in size from very small to very large and species life cycles and life history patterns are all different.

If you saw "swimming" (and Roger provided the correct description for swimming) versions they were larvae. Also, check out Roger's site as he has listed some excellent references that are fly fisher friendly e.g. McCafferty's book, with regard to learning about aquatic insects. I can also recommend Merrrit and Cummins as another good reference.

Rick