A method for producing a biogas is provided. The method includes the steps of providing a polyculture of aquatic plants to a growth system； continuously providing water, carbon dioxide, air and nutrients to the polyculture contained within the growth system； growing the polyculture for a time sufficient to produce an aquatic plant-based biomass； withdrawing a portion of the aquatic plant-based biomass contained within the growth system； and treating the withdrawn aquatic plant-based biomass to produce a biogas.
