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References:

Manual of Nearctic Diptera has a key to larvae. It is now available online. Volume 1 has the key to families, and this will probably be a Cyclorrhapha with family treatment in Volume 2.
http://www.esc-se...fcmono.php

Merritt and Cummins, An Introduction to the Aquatic Insects of North America has another key to all stages of aquatic insects. This is not available free online but Google Books will serve you excerpts.