After you get Lapras added to your Ride Pager, you can explore Melemele Sea, near the Pokémon Research Lab on Melemele Island.
New Things Near the Pokémon Research Lab
When you go to the Pokémon Research Lab on your way to Melemele Sea, you will find two Corsola. Talk to them to discover that one is hurt. No matter which option you choose, a Beauty will arrive and give you a Wide Lens.
There is a green sparkle to the right of the Pokémon Research Lab that you can collect with the Zygarde Cube.
Ride Lapras from the beach near Pokémon Research Lab to enter Melemele Sea.
Near the beach, you can battle Swimmer Yasu, who has a level 18 Tentacool.
There is an island in the upper-right of Melemele Sea where you can find Soft Sand.
Southeast of that island, there is a Super Repel underwater.
Near the Super Repel, you can battle Swimmer Kalani. He has a level 18 Wishiwashi and a level 18 Barboach. You get 432 Pokédollars for winning.
You will find some rocks southeast of here that you can't break right now.
If you go southwest, you can battle Swimmer Kelsie. She has a level 18 Finneon. You get 432 Pokédollars for winning.
Farther southwest, you can battle Swimmer Shelby. She has a level 18 Corsola. You get 432 Pokédollars for winning.
Keep going west to reach the western side of Melemele Sea.
In this area, you can battle Swimmer Jade. She has a level 13 Goldeen. You get 312 Pokédollars for winning.
Farther west, you can battle Swimmer Portia. She has two level 18 Luvdiscs. You get 432 Pokédollars for winning.
There is a small beach near Portia where Stoutland can help you find a hidden Rare Candy.