Photo source: Charlotte County
Grass carp are freshwater fish that feed primarily on aquatic plants. In the 1970s, they were introduced to a number of lakes and ponds in Florida as part of an experimental effort to control aquatic weeds, particularly the exotic plant Hydrilla (Hydrilla verticillata). The goal was to use these herbivorous fish to "graze down" nuisance plants.
Fortunately, the fish had a healthy appetite for Hydrilla and other types of nuisance aquatic plants. There was one drawback however; when over-stocked, grass carp consumed virtually every plant in a lake or water resource. Now, after several years of trial and error, it has been shown that, when stocked in appropriate numbers, grass carp can provide a low-cost, long-term, herbicide-free way of controlling nuisance plants.
IMPORTANT: There are potential problems associated with using grass carp as a form of aquatic plant control in a lake. Be sure to read the "Caveats and Limitations" section below for more information. Also, only triploid grass carp may be released into Florida waters and a permit must ALWAYS be obtained from the Florida Fish and Wildlife Conservation Commission (FWC) before doing so, even in private waters: https://myfwc.com/wildlifehabitats/habitat/invasive-plants/grass-carp/