Banna virus, whose genome is composed of 12 segments of double-stranded RNA, is a member of the genus Seadornavirus in the family Reoviridae and is thought to be an emerging mosquito-transmitted human pathogen in Southeast Asia. A novel phylogenetic relative of Banna virus (Balaton virus, BALV, JX947843-JX947850 and KC522611-KC522612) was identified using viral metagenomics in the intestinal contents of freshwater carp (Cyprinus carpio) in Hungary. The amino acid sequence identity of Balaton virus to homologous proteins of Banna viruses was 25-26 % for segment 12 (VP12) and 61-62 % for segment 1 (VP1), indicating that Balaton virus potentially represents a novel seadornavirus species. This study demonstrates that seadornaviruses are genetically diverse, not restricted geographically to Southeast Asia and present in an aquatic environment.