Bioassessment is an evaluation of the biological condition of a waterbody using biological surveys and other direct measurements of resident living organisms. Aquatic macroinvertebrates are important indicators of stream health: they are relatively long-lived, differentially sensitive to environmental stressors, and relatively easy to sample. This lesson is a hands-on introduction to the use of stream macroinvertebrates in assessing a stream’s biological condition. Students will learn how to (1) sample and identify stream macroinvertebrates and (2) conduct a rapid bioassessment to quantify ecosystem integrity based on the macroinvertebrate taxa that they collect. The lesson can be conducted with any number of students (although a second instructor would likely be needed for class sizes >20) and is appropriate for undergraduates of all levels.