A good friend of mine, a dentist, has a nice pond. So does my brother-in-law, who is also a dentist. They both have these plants in their gardens out in the backyard. The problem is that they grow so prolifically when it's warm that if they put a plant in their pond, a month later the pond surface is covered with them.
If they're living around a creek, which some of these people do, they take the plants, and instead of throwing them in the garbage, they throw them in the creek behind their house. These plants have these air vacuoles that allow them to float. You can watch them float out into the Great Lakes.
An undergraduate at my school called me and said there was an invasive plant called water lettuce in his backyard. I didn't know anything about water lettuce, so I Googled it, and the first thing I came up with was this pond shop. I almost fell out of my chair. When I saw the species he was selling, I realized he was selling not only the two that we're dealing with, but also a whole series of other ones. So I now use this example. I gave a presentation to the provincial fisheries ministers last year, and I showed that every one of the nine species that this gentleman was selling was invasive either in Canada or in some other part of the world.