Provides information of many groups of invertebrates commonly found in the streams, lakes, ponds, and other freshwater environments of North America. Section 1 provides background information on the biology and ecology of freshwater organisms and environments and explains why and how invertebrates can be studied, simply and without complex equipment, in the field and the laboratory. Section 2 describes nearly 100 of the most common groups of invertebrates, and for each group a whole-body color illustration is provided along with brief text pointing out the most important features that identify members of the group. Section 3 contains in-depth descriptions of the life history, behavior, and ecology of the various invertebrate groups, and explains their important ecological contributions and relationships in humans.