Nurse Joy runs a Pokémon Center nearby, which is built directly over an underwater spring. She explained that the area floods once every twelve years, helping to keep the Center's water supply filled. Gan Gogh, an artist, first traveled to the area 24 years ago, and he visits every twelve years to witness the mysterious Rainbow Lights. He stays at the Center, which has a perfect view that overlooks Remoraid Mountain. The cause of the floods and Rainbow Lights were revealed to be the Remoraid living atop Remoraid Mountain.
Ash and his friends stumbled across a set of ancient ruins left by the Colossal Tree Tribe also known as the Remoraidians, a group of people who carved and built large structures out of wood. The Remoraidians had to abandon their large city centuries ago after they cut down too many of the forest's trees and the rivers dried up. The Remoraid Mountain area remains a desolate wasteland littered with fossilizedRemoraid.
Remoraid Lake (Japanese: テッポウ池Teppouo Pond) is a dried-up lake that sits on top of Remoraid Mountain. It is dried up because of the actions of the Ancient Colossal Tree Tribe, which were there centuries ago. They loved the Remoraid that lived in the lake, and were also known as the Remoraidians. Near the mountain are the Ancient Colossal Tree Tribe ruins, which come from the tribe cutting down all of the trees from nearby forests and mountains, for miles around, in order to create a magnificent city. After all of the trees were cut down, the lakes and rivers dried up and the earth turned to dust. The Remoraidians left because of lack of food and water, but the Remoraid stayed and burrowed into the lake bed
Ash, Misty, Brock, Team Rocket, and Gan Gogh walked up to the lake bed to investigate some mysterious rainbow lights that appeared above the lake and found a gigantic ice pillar in the center of the lake bed. They later found out that the Remoraid use Water Gun every twelve years to fill the lake enough to swim around in and also, along with Ice Beam, to make the ice pillar even bigger. When the sun melts the ice pillar, the water vapor created from the melting ice refracts the sun light and creates the Rainbow lights as well as flooding the nearby lakes and rivers. The Remoraid are also adept at avoiding capture; should one be targeted with a Poké Ball, the entire school will surround it, causing the Ball to fail, as a Poké Ball will not work on more than one Pokémon at once. The Remoraid swim away to replenish their water supply and return, with hopes to bring back the green to the surrounding area. One of the rivers leads to an underwater lake right below the Pokémon Center; Nurse Joy uses it for water.