Aug 17, 2006 — Last year, the Great Lakes Radio Consortium asked 28 scientists and stakeholders to rank the major environmental issues affecting the region. The GLRC then sent a team of reporters throughout the region to explore these issues in-depth. The experts agreed that invasive species top the list. There are more than 160 non-native species in the Great Lakes and St. Lawrence Seaway. If they do harm to the ecosystem or the economy, they're labeled "invasive." Different species came in different ways - at different times. David Sommerstein looks at how some of the earliest invaders got into the region's waters.