After you make it through Route 5 and defeat Gladion on the way, you reach Brooklet Hill.
Meet Captain Lana
Up ahead, you find Lana, the captain of Brooklet Hill. Lana asks you to follow, so go across the wooden bridge. On the other side, go downward to find a Net Ball.
Talk to the fisherman to battle Fisherman Ernest. He has a level 16 Barboach and a level 17 Goldeen. You get 544 Pokédollars for winning.
Go upward, then to the left. In the southeast part of the grass, there is a hidden Elixir.
Go downward from the grass and you will find Lana again. Lana will add Lapras to your Ride Pager and ask you to investigate the splashing in the middle of the water.
Before getting in the water, go to the left to find an X Sp. Atk.
You can talk to the girl nearby to battle Backpacker Mikiko. She has a level 17 Fletchling. You get 408 Pokédollars for winning.
Then go downward from Lana and go to the end of the pier. You can talk to the fisherman to battle Fisherman Herbert. He has a level 17 Poliwag. You get 544 Pokédollars for winning.
Check on the water and you will be asked if you want to ride a pokémon. Say yes to get into the water on Lapras. Go to the rippling water and you find a level 17 Wishiwashi. Try to catch it if you can.
Afterward, there will be more splashing up ahead, so go southwest in the water and get out of the water there. Go to the left to get a Revive.
There is a Poké Finder spot near where you got the Revive.
Go southeast from there. There is a Max Repel hidden between the two sections of grass.
Up ahead, you meet Lana again. Check on the water to get in, then go to the rippling water in the middle of the pond. It's another Wishiwashi, this time level 18.
Afterward, Lana goes to the southwest of this pond.
Go southeast from where you fought the Wishiwashi and get out on the grass there. Follow the path to find TM55 Scald.
You can battle a fisherman near where Lana went. It's Fisherman Carl. He has a level 16 Magikarp and a level 17 Magikarp. You get 544 Pokédollars for winning.
Go southwest and you find Lana, who claims that Kyogre lives in Brooklet Hill, then says it was a joke. Go to the end of the path and go to Lana to enter the Totem's Den.
Totem's Den
Go up to Lana and your trial will begin. You won't be able to catch pokémon here until after you complete the trial.
Before you get into the water, go to the left along the sand to find a Hyper Potion.
Then get in the water and go to the splashing water in the middle. You will battle Totem Wishiwashi.
After you win, the trial is complete, and Lana gives you Waterium Z, which you can give to pokémon that know Water-type attacks.
Lana also gives you the Fishing Rod. You can use it at rocks under the water. Press A as soon as an exclamation mark appears. Lana also gives you 10 Dive Balls, which increase the chance of catching pokémon that you encounter while fishing.
If you wish, Lana can take you to the Pokémon Center on Route 5. If you say No, you can stay here to explore Brooklet Hill more.
Lana tells you that the next trial is Kiawe's trial, at Wela Volcano Park.
Now that you have a new Z-Crystal, the Poké Mart will add Revives and Honey to their selection.
Now go southeast to Paniola Ranch. Keep going south and you will battle Pokémon Breeder Amanda. She has a level 14 Lillipup and a level 15 Growlithe. You get 600 Pokédollars for winning.
Go through the grass behind her to find a Heal Ball. There is also a Big Mushroom hidden in the grass.
Go south from the Pokémon Breeder and you will find the Sudowoodos that Lana was talking about. Check on the Sudowoodos, and instead of battling you, they run away to Battle Royal Dome. The boy nearby gives you a Mystic Water, which makes a pokémon's Water-type moves 20% stronger if the pokémon holds it.
Go south to enter Route 6.