Transmission of antimicrobial-resistant bacteria among humans, animals, and the environment is a growing concern worldwide. The distribution of an international high-risk fluoroquinolone-resistant clone, ST131, has been documented in clinical settings. However, the transmission of ST131 from humans to surrounding environments remains poorly elucidated. To comprehend the current situation and identify the source of ST131 in nature, we analyzed the genetic features of ST131 isolates from the aquatic environment (lake/river water) and wildlife (fox, raccoon, raccoon dog, and deer) and compared them with the features of isolates from humans in Japan using accessory and core genome single nucleotide polymorphism (SNP) analyses. We identified ST131 isolates belonging to the same phylotype and genome clusters (four of eight clusters were concomitant) with low SNP distance between the human isolates and those from the aquatic environment and wildlife. These findings warn of ST131 transmission between humans and the surrounding environment in Japan.