I'm pretty sure she's referring to the Asian Carp becoming a massively annoying and costly invasive species in the Mississippi River. It is like she said, in the 1970s a bunch of fish farmers in the south brought in carp to clean their ponds (they feed on plankton and algae and microorganisms). But the carp thrived, and various factors including flooding caused them to escape the ponds and enter the Mississippi, where they have been swimming upstream and infesting other rivers and lakes for decades. The U.S. government has spent a decade trying a bunch of different tactics to prevent their entry into the great lakes - dams, gates, electrified fences, and mass poisonings. According to this article, in the Illinois River, which is connected to the lakes, 9 out of every 10 fish are Asian Carp. They wreak havoc on fishing and tourism, and are only eight miles away from Lake Michigan. One way of stopping them, closing the Chicago Lock, would cause at least a billion dollars in lost or wasted money from barges having to transfer loads back onto land. There has been a hundred million dollars spent in the past few years to examine the issue nationwide (they are now found in 23 states), to attempt to mitigate or remove them. All because some fish farmers tried to save a bit of money cleaning their ponds by changing one element of the local ecology.
Sorry I blew your cover, whoever wanted to hide that they live by any of the thousands of miles of rivers and lakes effected.