Rare aquatic Pokemon locations
Defeat the Wishiwashi Totem Pokemon on Akala Island to get the Fishing Rod. Then, go to the indicated fishing spot to catch the corresponding aquatic Pokemon. Make sure to bring lots of Pokeballs when fishing. For better results, save Lure Balls (given by Samson Oak on Blush Mountain) to increase your chances of catching Wild Pokemon while fishing. Unfortunately, these Pokeballs are not available to purchase — so use Lure Balls wisely. Alternatively, you can use Dive Balls which increases your catch rate versus water type Pokemon while swimming or fishing. Those are sold for $1,000 each. Note: Pokemon will only appear at fishing spots with bubbles. You can reset the fishing spot by leaving and re-entering.
Barboach: Enter Seaward Cave from Melemele Meadow on Melemele Island (enter the small hole south as you enter the yellow field of flowers). Once you are inside, go left to the small pond of water. Jump onto Lapras to find the single fishing spot. There is a 50% encounter chance. Barboach is a water/ground dual type that evolves into Whiscash at Level 30. Getting Whiscash is the main reason to catch this Pokemon.
Bruxish: On Route 13 on Ula’ula Island, enter the trailer park from Tapu Village, and proceed down the path south from the oasis in the center. Down on the coast, travel right from the old man, and right of the Trainer Tips sign, to see the fishing location. There is a 20% encounter chance. Bruxish is a water/psychic dual type that can also be found on the Secluded Shore, or on Route 14 and Route 15.
Chinchou: Search for the two fishing spots on the east coast of the Akala Outskirts area on Akala Island, near a fisherman. Go to the more northern of the two fishing spots to get this Pokemon. There is a 20% encounter chance. Chinchou is a water/electric dual type that evolves into Lanturn at Level 27.
Corsola: Start from Hau’oli City beach on Melemele Island, and use Lapras to swim southeast in the Melemele Sea to a cave entrance blocked by boulders that only Sharpedo can break. To the left of the cave entrance is a fishing hole. There is a 20% encounter chance. Corsola is a water/rock dual type that does not evolve into any new forms. To easily reset the spot, simply use Sharpedo to bust into the nearby Ten Karat Hill cave.
Dhelmise: In Seafolk Village on Poni Island, enter the Steelix houseboat and go through the lower door to the porch/balcony exterior with a view of the fishing spot. You have to coax it from its hiding spot in Seafolk Village. There is a 10% encounter chance. Dhelmise is a grass/ghost type that does not evolve.
Dratini: There is one fishing spot straight ahead after entering Poni Meadow from Poni Plains on Poni Island. There is a 10% encounter chance. Dratini is the first form of Dragonair. Dragonite is a dragon type introduced in Gen 1. It is a pseudo-legendary Pokemon, but it is powerful and grows in strength quickly.
Feebas: Just as you enter Brooklet Hill on Melemele Island, go down the ramp to the bridge. Jump onto Lapras and ride south to find the fishing spot that is only accessible from the water. There is a 10% encounter chance. Feebas evolves into Milotic when traded while holding a Prism Scale.
Lapras: In Poni Wilds on Poni Island (west of the Seafolk Village), there is a 5% you will encounter Lapras while swimming in the water to the left of the beach. This is not a fishing location. Lapras is an ice/water dual type that does not evolve. Lapras is most well known for its Swim HM ability, helping trainers easily cross water. Lapras can still transport trainers with the Poke Ride system.
Mareanie: This Pokemon is found in the same fishing spot as Corsola. Typically, Corsola will summon Mareanie when it calls for help. The encounter chance is unknown. Mareanie is a water/poison dual type that evolves into Toxapex and becomes much deadlier.
Relicanth: On the beach in Poni Wilds on Poni Island, locate the final trainer (the Dancer) and walk directly left. Ride Lapras to the first fishing spot directly left (and slightly below) that trainer. There is a 10% encounter chance. Relicanth is an ancient water/rock dual type that does not evolve.
Sharpedo: It is found just south of the entrance to the Ruins Of Hope in Poni Breaker Coast on Poni Island. There is a 10% encounter chance. Sharpedo is a brutal/dark dual type that evolves into Carvanha at Level 30, and has a Mega form when equipped with Sharpedonite. Note: To get Carvanha without using Wonder Trade, breed Sharpedo.
Shellder: Exit Seaward Cave to reach Kala’e Bay on Melemele Island. Just as you exit the cave, use the fishing spot north near the shore. You will not need to use Lapras to reach this spot. There is a 20% encounter chance. Shellder evolves into Cloyster with a Water Stone.
Wishiwashi: This Pokemon is found in the same fishing spot as Chinchou. There is a 30% encounter chance. Wishiwashi unlocks the Schooling ability at Level 20. In School form, Wishiwashi joins up with a horde, turning the swarm into one giant fish school body. It changes the look of the Pokemon while in its new body. Wishiwashi does not evolve.