Surf allows Ditto to travel across water in Pokémon Pokopia.
Ditto learns useful moves from Pokémon it befriends, and those moves expand how it can explore and restore the world. Surf is the water-travel ability: it lets Ditto move across watery terrain and reach areas that cannot be crossed on foot.
This mechanic fits Pokopia's broader design, where Pokémon abilities function as environmental tools. Players use different moves to cultivate habitats, clear obstacles, water plants, and travel through the map. The goal is not simply to win battles but to make the world livable and connect different areas of the settlement.
Surf can be confused with Dive, especially because Pokopia later received an update adding underwater exploration. Dive allows Ditto to move underwater and reach otherwise unexplorable regions, while Surf is the move associated with crossing the surface of water. Water Gun is another aquatic move, but its described use is hydrating plants rather than transportation.