Question: how did zebra and quagga mussels get introduced into the great lakes?
Answer: Zebra and quagga mussels were introduced to the Great Lakes from the Caspian and Black Sea region in the 1990s through ship ballast water. Since their introduction, they have spread by attaching to boat hulls, motors, and engine cooling intake lines or pipes, or by surviving as larvae in boats' water-holding areas.