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Although the Great Lakes boast a $7 billion/year fishing industry, there is one fish that's not welcome here: the Asian carp. The invasive silver Asian carp can weigh up to 100 pounds and eat 20 percent of their weight each day in plankton; they're capable of interrupting natural biological systems and interfering with chemical processes. This fish has not been sighted in the Lakes themselves, but they were tracked to the century-old man-made canal that connects the Great Lakes with the Mississippi River watershed. Some scientists predict that if the silver carp infiltrate Lake Michigan and attain breeding populations, "the fish would ultimately upend the entire ecosystem in the lakes that make up a fifth of the earth's freshwater surface." Other scientists claim that we cannot accurately foresee how silver carp will grow and reproduce in the Great Lakes ecosystem.

This is another example of the unexpected environmental consequences of human actions. The canal between the Mississippi River and Lake Michigan was built over a hundred years ago; it has served as a channel for human beings, a route for trading, a medium for sewage transport, and a passage for unwanted nonnative species, such as the silver carp and zebra mussels. Today, the canal remains controversial. Barges carry almost 17 million tons of material on this waterway annually; if the canal's yearly load was transported via land, an additional 1.3 million trucks would be needed. Once again, human interests and the natural environment are clashing. How can we prevent the silver carp from infesting the Great Lakes and potentially destroying the entire ecosystem, without risking the important economic gains from the Lakes' resources and industries?

Photo courtesy of Kate Gardiner