When Gretchen, Jason, Mark, and Daphne find their favorite swimming hole filled with green slime, they are horrified. A mysterious, almost magical naturalist named Riparia helps the children understand why the water became polluted—and together they figure out what they can do to bring clean water back to the river they all love. This lively story about non-point source pollution is filled with both information and action. Realistic, lush illustrations by Olga Pastuchiv illuminate the children's passion for their river and the ecosystem it supports.