Acoustic topological systems explore topological behaviors of phononic crystals. Currently, most of the experimentally demonstrated acoustic topological systems are for airborne acoustic waves and work at or below the kHz frequency range. Here, we report an underwater acoustic topological waveguide that works at the MHz frequency range. The 2D topological waveguide was formed at the interface of two hexagonal lattices with different pillar radii that were fabricated with metal additive manufacturing. We demonstrated the existence of edge stages both numerically and in underwater experiments. Our work has potential applications in underwater/biomedical sensing, energy transport, and acoustofluidics.