This was a concern because Asian carp grow to large sizes (50-110 lbs.) and eat up to 20% of their body weight daily, possibly out competing native species for food or habitat resources. These big eaters could unravel the food web by consuming plankton needed by smaller fish that feed sport fish, such as bass and walleye. Silver carp can also leap really high out of the water, appearing to almost fly. They have been known to injure people if they land on them. In 1996 an Asian carp was reported for the first time on the St. Croix River. Since then an occasional catch of bighead carp have been reported in 2011 and 2012.
Multiple federal and state agencies have joined together to prevent or decrease the impact of Asian carp on the St. Croix, Mississippi and Minnesota Rivers. In November 2011 an Action Plan was finalized. The threat was brought home in in 2011 when eDNA testing aimed at detecting species of Asian Carp on the St. Croix River, suggested their presence for several miles downstream of the hydroelectric dam at St. Croix Falls, Wisconsin. Asian carp were detected using a new technique that analyzes water samples for traces of fish, such as body fluids, scales, etc. Results pointed to the Asian carp species called silver carp (known as the flying carp for their leaping ability) as the fish in this section of the river. To date, no physical specimen of silver carp has been found in the St Croix. (MN DNR Press Release) See the report, eDNA Surveillance of Asian Carp on the St. Croix and Mississippi River (PDF, 500kb) and sampling map for detailed findings. (Funding for the study has been provided by the Mississippi River Fund and St. Croix National Scenic Riverway Fund of the St. Croix Valley Foundation.)