A novel bacterial strain, designated NA-$09^T$, was isolated from a freshwater sample collected from the Cheonho reservoir, Republic of Korea. Colonies were creamy-white pigmented, translucent, and circular with convex shape. The isolate was Gram-staining negative, strictly aerobic, motile, and rod-shaped. The 16S rRNA gene sequence analysis revealed that strain NA-$09^T$ belonged to the genus Arenimonas and showed the highest sequence similarities with Arenimonas malthae CC-JY-$1^T$ (95.4%), A. oryziterrae $YC6267^T$ (94.9%), A. composti P2-12-$1^T$ (94.8%), and A. donghaensis H03-$R19^T$ (94.1%). The major fatty acids were iso-$C_{16:0}$ (20.8%), iso-$C_{15:0}$ (16.9%), summed feature 1 (13.2%), and iso-$C_{16:1}{omega}7c$ alcohol (10.2%). The major isoprenoid quinone of the isolate was ubiquionone-8. On the basis of the data from the polyphasic characterization, the strain NA-$09^T$ represents a novel species, for which the name Arenimonas aquaticum sp. nov. is proposed (type strain NA-$09^T$ =KACC $14663^T$ =NBRC $106550^T$).