Although surf is not required to clear this gym, it is recommended. For those who are unable to use their pokemon to navigate around water, surfboards are provided. This is a much slower method of travel, however.
As one can assume, the entirety of the gym is filled with water save for the entrance, which is decorated with sand and shells to make a mock shore. Underwater fans are used to make fake currents and riptides in the "ocean" to create a maze.
The trainers in this gym are swimmers and surfers. Tia only accepts confident swimmers as her trainers and has a strong relationship with all of them.