This excellent report neglected to mention that the entire problem of invasive alien species was started by the Great Lakes - St. Lawrence Seaway, opened in 1959. The Welland Canal was 'further straightened', according to the website, in 1973. Surely many viewers are younger than this system of canals and locks, and may not realize, especially living in Chicago, how much anti-Nature engineering is involved. Even birchbark canoes had to portage. Can we be confident that ballast-purging will be enough? What about alien species on the hulls of oceangoing ships? Is it possible we'll need to keep the Great Lakes fleet separate from the oceangoing ships, and transfer the cargo, to stop the invasions finally?