A bacterial strain, designated Agd-32T, was isolated from a water sample taken from the Agongdian Reservoir in Taiwan and characterized using a polyphasic taxonomy approach. Cells of strain Agd-32T were Gram-stain-variable, aerobic, motile by means of peritrichous flagella, endospore-forming, rod-shaped and surrounded by a thick capsule. Strain Agd-32T contained anteiso-C15 : 0 and C16 : 0 as the predominant fatty acids. The major isoprenoid quinone was MK-7, and the polar lipid profile consisted of phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol, one unidentified aminophosphoglycolipid, one unidentified glycolipid, one unidentified phospholipid and one unidentified lipid. The DNA G+C content of the genomic DNA was 56.0 mol%. Strain Agd-32T contained meso-diaminopimelic acid in the cell-wall peptidoglycan. Phylogenetic analyses based on 16S rRNA gene sequences showed that strain Agd-32T belonged to the genus Paenibacillus and was most closely related to Paenibacillus tarimensis with sequence similarity of 96.1 % and less than 95.9 % sequence similarity with other members of the genus. On the basis of the phylogenetic inference and phenotypic data, strain Agd-32T should be classified as a representative of a novel species, for which the name Paenibacillus lacus sp. nov. is proposed. The type strain is Agd-32T (=BCRC 80902T=LMG 28836T=KCTC 33691T).