The Great Lakes are under threat from the Asian carp, an invasive fish species that has colonized much of the Illinois river. The Illinois river is a separate waterway than the Great Lakes system, but since the 1800s the two have been linked by canals running through Chicago (and responsible for Chicago's initial strategic importance as a transport hub). The Asian Carp are now migrating up these canals, and despite certain efforts at blocking their advance, it is believed that eventually the fish will enter the Great Lakes, and very probably wreak ecological havoc there. The Asian carp is a filter feeder, meaning that it strains water through its mouth as it swims. This removes all the algae and plankton from the water, starving other fish species.
Aside from existing measures like electronic and chain fences in and around infested canals, an effective manner of preventing the Asian carp's progress into the Great Lakes would be overfishing them. Overfishing is a problem when a native, valuable species is harvested to the point of population crash. But in the case of an invasive species, overharvesting can lead to a desired population decrease. It may not be able to completely eliminate the species, but an intense harvesting pressure on Asian carp would help to check their existing population, and decrease the likelihood and speed of their advance into the Great Lakes.
However, the Asian carp does not enjoy great demand as food. It is said to have a bland or even disagreeable flavor, and the abundance of bones makes it difficult to process. Even sport fishermen won't pursue the fish, because as a filter-feeder it doesn't bite bait.
But the Asian carp could be very well-suited as an agricultural input. The fish could be netted en masse and ground up. The oil from the ground fish could be extracted and used for human or animal health supplements, and the remaining protein-rich meal channeled into a number of uses. Asian carp meal would be an excellent component of feed for many farmed species of livestock and fish. Asian carp meal could also be sold to farmers as a fertilizer rich in nitrogen and phosphorus. The meal could be sold fresh to farms along the Mississippi and Illinois rivers, and dehydrated into a powder for sale farther afield.
The Carp Harvest project would hence fight against the infestation of the Great Lakes by an alien species, while replacing part of the synthetic fertilizers used in the Midwest. Fertilizer runoff feeds algae, which feed Asian carp, so to turn that carp into fertilizer is to capture nutrient runoff and re-apply it to fields in a more stable, organic form. Hence the ecological health of the Great Lakes, Midwestern farm fields, and the Gulf of Mexico would all be improved by this project.