A 3-day field investigation where middle schoolers visit an aquatic area and collect snails. These are examined, the species identified, and the body parts and characteristics studied and recorded. Then the snails are returned to their homes. The next day, they return to the same area to find and count snails and mark them with a dot of nail polish. The third day, they collect and count snails again, and record how many of the marked snails they find as well. From these investigations, they use a formula to calculate the total snail population.