These four species of fish were introduced to the U.S. in the 1970's to control algae, weed, and parasite growth in aquatic farms, weeds in canal systems, and as one form of sewage treatment. These captive fish eventually escaped into the Mississippi River basin and established breeding populations. Asian carp are slowly making their way up the Mississippi River and its tributaries, and have been found as far north as Minnesota, including individual silver and bighead carps within the Mississippi National River and Recreation Area. There is no indication that they are spawning here, but they still represent a threat to our valued aquatic ecosystems.