Zebra mussels are native to freshwater lakes and rivers of western Russia. Canal building to facilitate shipping around the turn of the eighteenth century allowed them to spread throughout Europe and Britain. In the late 1980s, Zebra mussels were introduced to Lake Erie in North America, likely through ballast water discharged from transoceanic ships. Within a few years, they had spread throughout the Great Lakes and into inland waterways, where they clog the water intake structures for power plants and water treatment plants, alter ecosystems, and threaten fish and wildlife. Did shipping provide an externality in this respect? What type?