Heading west from Route 130, Route 131 passes by a pair of Trainers (in Emerald only) before coming to the mouth of the winding channel that leads to the Sky Pillar. In Pokémon Ruby and Sapphire, there is a female Swimmer west of the channel mouth. In all Hoenn-based Generation III games, there are two more Swimmers to her west.
Northwest of the second Swimmer in this group is a lone Swimmer in the middle of the route. To his northwest is a Sis and Bro Trainer team. South of the duo in Pokémon Emerald is yet another Trainer.
Pacifidlog is a short swim to the west from this point.
During the Delta Episode, after meeting Wallace outside the Cave of Origin in Sootopolis City, Wallace will be here after having just broken the seal. However, he informs the player that he cannot allow them entry unless they defeat him in battle again. After he is defeated, he leaves and grants the player access.