Cilj istraživanja je utvrditi prinos bioplina i metana iz gnojovke s dodatkom tri vrste vodenih biljaka (Spirodela polyrhiza, Azolla caroliniana i Lemna minor). Uzgoj tradicionalno korištenih biljaka (npr. kukuruz, uljana repica) za dobivanje biogoriva zahtijeva obradive površine, dok se vodene biljke, kao alternativa, mogu prikupiti iz prirode, a zbog jednostavne građe, brzine rasta i povoljnog kemijskog sastava mogu se bez pred-tretmana koristiti kao osnovna ili dopunska sirovina u bioplinskim postrojenjima. Četiri uzorka (kontrola i tri vrste vodenih biljaka) u tri ponavljanja povrgnuta su anaerobnoj digestiji. Različite vrste proizvode različite količine bioplina u odnosu na kontrolu (od 504,83 do 881,62 mL g-1 S.T.). Udio dobivenog metana iznosi od 57,96 do 60,63 % u zavisnosti od biljne vrste. Ovo ukazuje na izuzetan potencijal korištenja ovih vrsta za dobivanje bioplina i metana.; The aim of the study is to determine the yield of biogas and methane from slurry with the addition of three species of aquatic plants (Spirodela polyrhiza,Azolla caroliniana and Lemna ninor). Cultivation of traditionally used plants (eg.corn, oilseed rape) to produce biofuels requires arable land, while aquatic plants,as an alternative, can be collected from nature, and due to simple structure, growth rate and favorable chemical composition, they can be used as a primary or supplementary raw material in biogas plants without any pre-treatment. Four samples (control and three aquatic plant species) in three replicates were subjected to anaerobic digestion. Different species produce different amounts of biogas compared to the control (from 504.83 to 881.62 mL g-1 DM). The methane content is from 57.96 to 60.63% depending on the plant species. This indicates the tremendous potential of using these species of aquatic plants to produce biogas and methane.