A bacterial strain, designated TTM-2T, was isolated from a water sample taken from the Caohu River in Taiwan and characterized using a polyphasic taxonomic approach. Cells of strain TTM-2T were Gram-stain-negative, aerobic, poly-�]-hydroxybutyrate-accumulating, non-motile, rod-shaped and covered by large capsules; they formed light pink colonies. Growth occurred at 15-37 �XC (optimum, 30 �XC), at pH 4-8 (optimum, pH 6) and with 0-1 % (w/v) NaCl (optimum, 0.5 %, w/v). Phylogenetic analyses, based on 16S rRNA gene sequences, showed that strain TTM-2T belonged to the genus Mucilaginibacter. The sequence similarities between the 16S rRNA genes of strain TTM-2T and the type strains of other species of the genus Mucilaginibacter ranged from 93.6 to 97.4 %. The closest relatives of strain TTM-2T were Mucilaginibactersoli R9-65T (97.4 %) and Mucilaginibactedefluvii A5T (97.1 %). The predominant fatty acids were iso-C15 : 0 (36.9 %) and summed feature 3 (C16 : 1�s7c and/or C16 : 1�s6c; 33.7 %). The polar lipid profile consisted of phosphatidylethanolamine and several uncharacterized aminophospholipids and phospholipids. The major isoprenoid quinone was MK-7. The DNA G+C content of the genomic DNA was 46.6 mol%. The DNA-DNA relatedness of strain TTM-2T with respect to species of the genus Mucilaginibacterwith validly published names was less than 70 %. On the basis of the phylogenetic inference and phenotypic data, strain TTM-2T should be classified as a novel species, for which the name Mucilaginibacter fluminis sp. nov. is proposed. The type strain is TTM-2T (=BCRC 80785T=LMG 28455T=KCTC 42274T).