The key for Colepotera can be found in Chapter 12 of the Guide to Aquatic Invertebrates of the Upper Midwest, pages 145-158. Once you have keyed out your insect, you can use the photographs on this website to verify your identification. If you click on the link to the family on the right, you will be directed to a page that has photographs of that family along with close-up photos of their identifying characters.
Coleoptera adults can be recognized primarily by the presence of heavily sclerotized fore wings (elytra) which lack veins and cover the membranous hind wings. In addition, the entire body is generally hardened and three pairs of segmented legs are present. Adult Coleoptera can be separated by characters such as the shape of the eye, the hind coxae, and the antennae.