The leaf liquid should be very dense with leaves. Swirl several times a day for 3 or 4 days. If not used at this time refrigerate up to a month. As a class or in cooperative groups generate a hypothesis. List the plant extracts plus a plain water control.
Students rank each plant they choose based on field observations.
Choose seed for bio-indicator. These could be seeds from one or more wetland plants or a quick growing seed like a radish. Label petri dishes. Measure enough plant extract water onto the paper towel to soak it. Be sure the plant extract used on the seeds matches the label on the petri dish.