An actinomycete, strain L1505(T), was isolated from a limnetic lake sediment and found to have morphological, biochemical, physiological and chemotaxonomic properties consistent with its classification in the genus Williamsia. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain L1505(T) formed a distinct lineage within the genus Williamsia. The isolate belonged to a cluster containing W muralis MA140/96(T), W. marianensis MT8(T) and W faeni N1350(T), with which the isolate shared 99.0-98.2% 16S rRNA gene sequence similarity. Genotypic and phenotypic data also indicated that the isolate was different from known members of the genus Williamsia. On the basis of these data, strain 1505(T) is considered to represent a novel species of the genus Williamsia, for which the name Williamsia limnetica sp. nov. is proposed (type strain L1505(T)=DSM 45521(T)=NRRL B-24829(T)=KCTC 19981(T)).