Ballast water, which keeps ships upright and balanced, is discharged when a vessel moves from one body of water to another through canals or locks.

More than 21 billion gallons of untreated ballast water is discharged into U.S. waters each year. In the Great Lakes alone, the amount of potentially dangerous water dumped by transoceanic freighters amounts to about a billion gallons annually, roughly equal to 1,500 Olympic-size pools.

Untreated ballast discharges have resulted in the introduction of more than 180 aquatic invasive species into the Great Lakes. Other U.S. waters have been similarly affected.

In 2007, scientists estimated there were 500 million pounds of zebra and quagga mussels in Lake Michigan.

Billions of dollars in damage to fisheries, recreation and public infrastructure can be directly attributed to aquatic invasive species.

Mussels have clogged the filter screens of water treatment plants while mussel-fuled algae blooms have clogged water intakes and forced emergency shutdowns of nuclear power plants.

Even ocean freighters that report having no ballast on board – known as NoBOB ships within the industry – routinely carry billions of foreign organisms and pathogens in the muddy water sloshing inside their supposedly empty ballast tanks. Every time a freighter empties its ballast tanks, it leaves behind a potential biological time bomb.

The Clean Water Act of 1972 and the Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990 were intended to prevent the spread of invasive species but lax enforcement of the regulations has failed to stop the flow of foreign organisms into U.S. waters.

Asian carp is the latest in a long line of creatures from eastern European waters to invade the Great Lakes, following alewives, Eurasian ruffe, round gobies, spiny water fleas, bloody red shrimp and dozens of other destructive aquatic species. Asian carp represent a major threat to the Great Lakes since the fish consume huge quantities of plankton at the base of the food chain.

(A number of these facts derive from Jeff Alexander’s excellent expose, Pandora’s Locks, published by Michigan State University Press. Visit for more information.)