Same old Pokémon as in the rest of the sea. Hopefully your Repels haven’t ran out.
|Luvdisc||Water||Good/Super Rod||35% (Good), 60% (Super)|
|Magikarp||Water||Old/Good Rod||65% (Old), 60% (Good)|
|Wailmer||Water||Good/Super Rod||5% (Good), 60% (Super)|
Local Trainers Pokémon
|Ace Trainer Cornelius||2,340||Golem Lv. 39, Raichu Lv. 39|
|Fisherman Wayne||1,184||Wailmer Lv. 37, Seadra Lv. 37|
|Tuber Delmar||152||Luvdisc Lv. 38|
|Tuber Marlene||152||Luvdisc Lv. 38|
|Triathlete Isaiah||1,440||Starmie Lv. 36|
|Free Diver Mayu||1,560||Luvdisc Lv. 39, Luvdisc Lv. 39|
As you enter the Route, a big portion of it will be dominated to the south by that big circle thing you’ll sink into later. But first go east and battle the Ace Trainer.
Southeast of him is a Fisherman to fight (use the Dowsing Machine to find a Heart Scale near him), then a Tuber and some other Trainers further east. (To the curious, the name “Delmar” can be split into “del” “mar”, which - at least in Spanish - means “of the sea”.)
Surf onto the island west of the Fisherman and you can use the Dowsing Machine to find another Heart Scale . The Dive spot nearby - the small square one - has a Diver to battle and the Route’s underwater seaweed for Pokémon, so you know.
Aside from this, head to the big circle made of the shallows west of there. Enter the Dive spot inside the circle; underwater, examine the north-center part of the circle for an Adamant Orb , used to power up Dialga.
After that, go into the Dive area outside the circle (the gigantic Dive area) and enter the cave at the south side of said circle.