This semi-guided inquiry activity explores the macroinvertebrate fauna in water sources affected by different levels of pollution. Students develop their ability to identify macroinvertebrates, compare aquatic fauna from different sources of water samples, evaluate water quality using an index, document and analyze data, raise questions and hypotheses, and discuss other possible issues that could be investigated at a later time. These sets of activities were designed for freshman high school students but are applicable to middle school students as well.