$1:
A thin, underwater "electric fence" in a canal near Chicago, and vigilance by governments and citizens, are all that prevent a group of invasive fish species from disrupting aquatic ecosystems across the Great Lakes.
Four species of Asian carp, the grass, bighead, silver, and black, could readily move from the United States into Canada. Freshwater fisheries scientist Nick Mandrak, of the Great Lakes Laboratory for Fisheries and Aquatic Sciences (GLLFAS) in Burlington, Ontario, says that "people tend to think of Asian carp as semi-tropical. But I've seen them thriving under a metre of ice in frozen Russian lakes. They could survive right across Canada. And they can do great damage."