Cross the bridge and turn left to pick up a Net Ball and battle the fisherman.
Approach Trial Captain Lana. She will add Lapras to your Ride Pager to help you travel across water. Before following her to the next pool of water, jump on Lapras on the west side of the bridge, and swim back towards the entrance. You’ll find a fisherman on a peninsula who wants to battle.
Pick up the Rare Candy next to him. Head for the next area and Lana will explain the trial to you. Before jumping in the water, walk to the left, pick up the X Sp. Atk, and fight the trainer.
Walk to the other of the path and fight the fisherman on the bridge.
Jump into the water and ride over to the bubbling fountains of water. Once you defeat the Pokemon, have Lapras swim south, jump off and pick up the Revive, and take the path leading down to the next pool. Repeat the process but once you’re done, swim over to the east and fight the fisherman to the right.
Take the path down to the last pool of water. Before jumping on Lapras, walk over to the left and pick up the Hyper Potion.
Swim out to the last bubbling fountain of water and you’ll face Totem Pokemon Araquanid.
Trial Captain Lana rewards you with Waterium Z, a Fishing Rod, and ten [Poke Balls|Dive Ball]]s. That completes your first trial on Akala Island! You can choose to be escorted back to the Pokemon Center on Route 5, or stick around to test out your new Fishing Rod.