There are four non-native carp species that threaten the St. Croix. On September 16, 2014, a bighead carp was captured at the mouth of the St. Croix River. Silver carp, the carp species known for leaping out of water, have been caught in the Mississippi near the St. Croix, and their DNA was detected in the St. Croix in 2011. Both species consume huge amounts of plankton and detritus, and compete directly with native organisms such as mussels, larval fishes, and some adult fish. Black carp and grass carp have not been detected near the St. Croix, but are established lower in the Mississippi and pose a significant future threat to the St. Croix watershed.
In areas where they are well-established, silver carp took only a few years to out-compete everything else in the river and become the overwhelmingly dominant fish. This would be devastating to the St. Croix River’s outstanding fishery. In addition, silver carp are exceptionally prone to jumping when disturbed by motorboats, and have caused serious injuries to recreational boaters on other waters. Video footage shows 40-pound fish exploding from the river like popcorn. Abundant silver carp in Lake St. Croix would be extremely detrimental to recreational boating on one of the Midwest’s most popular waters.