Boaters on the Great Lakes often see clusters of small mussels stuck to docks, rocks, and even boats! Called zebra mussels, these organisms can cause people to cut their feet, filter out food for larval fish, and more. Through reading about how zebra mussels came to these freshwater lakes, readers learn what invasive species are and how they can cause great harm to native ecosystems. Facts about the spread of zebra mussels and efforts to stop this spread introduce readers to conservation and other science curriculum topics. Full-color photographs, fact boxes, and maps showing zebra mussel distribution augment readers' understanding.