Canal systems, ballast water from oceangoing ships, and seemingly little things such as fish stocking, bait bucket emptying, and trailering recreational boats all provide ways for non-native invasive species to infest North America’s aquatic environments. Using the Great Lakes—unwilling home to the sea lamprey, zebra mussel, round goby, and Eurasian ruffe—as a case study, this program takes a close look at the threats posed by aquatic nuisance species and how scientists, policymakers, and the public are working to prevent the further spread of these devastating invaders. San Francisco Bay, with its Chinese mitten crab problem, is also touched upon. (28 minutes)