Native to northern Europe, the spiny waterflea (Bythotrephes longimanus) was first discovered in Lake Huron in 1984, spreading to all the Great Lakes by 1987. Scientists think international cargo ships first carried the spiny waterflea to North America in their ballast water. The species has changed the food webs of the Great Lakes by causing declines in native zooplankton through direct predation, thus impacting sport and commercial fisheries. Credit: United States Environmental Protection Agency Great Lakes National Program Office