They largely feed on grasses and aquatic plants, foremost on Saccharum, Imperata cylindrica, Narenga porphyrocoma, Phragmites karka, Oryza rufipogon, Hygroryza and Hydrilla.
The Government has also embarked on using grass carp in aquatic weed eradication projects, such as Lakes Tutira, Opouahi and Waikopiro for Hydrilla and in Lakes Swan, Heather, Kereta for Common Hornwort (Ceratophyllum).
Insects used as biological pest control for this plant include weevils of the genus Bagous and the Asian hydrilla leaf-mining fly (Hydrellia pakistanae).
Other than extensive diversions, exotic introduced, fast-growing and water-consuming plants, such as water hyacinth and hydrilla, are also leading to reduced flows.The United States government has recently attempted to slow or stop the progress of these weeds by introducing insects and fish that feed on the invasive plants.