If you Surf north from Route 12: Fourrage Road, you find the watery path of Azure Bay.
Wild Pokémon
In Azure Bay, you might encounter Tentacool, Lapras, or Mantyke while surfing. In addition, if you use the Old Rod to fish, you will find Luvdisc. If you use the Good Rod, you may find Chinchou or Remoraid. With the Super Rod, you may find Alomomola, Lanturn, or Octillery. If you use Rock Smash in this area, you might find Dwebble or Binacle. In the grass, you might find Slowpoke, Exeggcute, Chatot, or Inkay. You might also have horde encounters with Slowpoke, Exeggcute, or Wingull.
Battle and Explore
Surf west from the entrance of Azure Bay to find Swimmer Kieren, who has a level 27 Remoraid, a level 27 Skrelp, and a level 27 Wailmer.
West of there, you find Swimmer Romy, who has a level 30 Slowpoke.
To the north, there is a small island with a Photo Spot. Talk to the old man to get Ampharosite.
On the island, you can battle Fisherman Ewan, who has a level 27 Clauncher and a level 29 Carvanha.
East of the island, you can battle Sky Trainer Indra, who has a level 31 Sigilyph.
West of the island, you find Swimmer Ilsa, who has a level 28 Corsola and a level 28 Lanturn.
North of the island, there is another small island. This one has some tall grass. There is a Big Pearl there.
Northeast of that island, there is a small island where you can use your Dowsing Machine to find a hidden Star Piece on the rock.
Surf west. There is another small island with a rock on it. However, there are no hidden items on it. Surf west until you reach the edge, then go south along the edge. To the right, there is a large island. You can land on the island from an opening on the left side.
In the north part of the tall grass, there is a Deep Sea Tooth.
Use the Dowsing Machine here to find a hidden Hyper Potion on a rock. Go south to find a Deep Sea Scale in the grass.
Go south to find TM81 X-Scissor.
Now leave the island and go north. There is a large sandy island with a sign on it. Use your Dowsing Machine here to find a hidden Heart Scale on a rock north of the sign.
Go north across the shallow water to find a Dive Ball.
To the north, you can battle Sky Trainer Elatal. She has a level 28 Fletchinder and a level 29 Pelipper.
Surf east. There is an island in the center of north Azure Bay. Go to the northeast corner of this island to find a Splash Plate.
On the front of this island, there is an entrance to the Sea Spirit's Den. It's empty right now.
When you're done exploring Azure Bay, you can go back to Fourrage Road.