Around 1900, civil engineers connected the Great Lakes to the Mississippi River Basin to let shippers access both waterways. But within the past 30 years, biologists and the Army Corp of Engineers have been trying to keep aquatic species from moving out of native habitats in the Great Lakes and into the Mississippi River Basin and vice versa. Currently, professional and amateur fishermen in the Great Lakes, along with the area’s tourist industry, are desperately seeking ways to prevent Asian carp from getting from the Mississippi into Lake Michigan, a gateway to the rest of the Great Lakes and St. Lawrence Seaway. One method being suggested are a series of locks with special provisions for keeping fish and other aquatic species from getting through.

Ships approaching these so-called Great Lakes and Mississippi River Inter Basin (GLMRIS) locks first pass over a series of passive electrodes that send enough current into the water to stun and repel fish and other aquatic animals. Then, once the vessel is in the locks and gates are closed at both ends, pumps suck out untreated water from the entry end while other pumps send treated water into the other end. This keeps the vessel afloat while the water is exchanged. Treated water consists of river or lake water that has been sent through screens small enough to remove any fish and animals. Then it is filtered through sand to remove eggs, seeds, and other small pieces of organic matter. Finally, the water is irradiated with UV light to kill the vast majority of any remaining microorganisms.

Once sufficient time has passed to allow all the water to be exchanged, the far gates open and the ship passes through, without any hitchhiking fish or plants. The Corp of Engineers estimate such a project could cost $15 billion and take 25 years.