A freshwater bacterium, designated IMCC1728(T), was isolated from a eutrophic pond. The strain was Gram-negative, chemoheterotrophic and facultatively aerobic, forming non-motile rods that contained poly-beta-hydroxybutyrate granules. Based on 16S rRNA gene sequence comparisons, the most closely related species to strain IMCC1728(T) was Methylibium petroleiphilum (97.0 % similarity). Phylogenetic trees generated using 16S rRNA gene sequences showed that this isolate formed an independent phyletic line of the genus Methylibium clade of the class Betaproteobacteria. The DNA G+C content of the strain was 66.2+/-0.4 mol%. The predominant cellular fatty acid constituents were C(16 : 1)omega7c and/or iso-C(15 : 0) 2-OH (43.1 %), C(16 : 0) (20.3 %), C(12 : 0) (13.4 %) and C(10 : 0) 3-OH (7.3 %). The strain contained Q-8 as the predominant ubiquinone. Several phenotypic characteristics, including flagellation, temperature range for growth and carbon source utilization patterns, differentiated strain IMCC1728(T) from species of the genus Methylibium. Therefore, it is proposed that strain IMCC1728(T) represents a novel species, Methylibium aquaticum sp. nov. The type strain is IMCC1728(T) (=KCCM 42364(T)=NBRC 102349(T)).