Walkthrough: Off the southern edge of Route 12 is Secluded Shore, a location where a number of Water Pokemon and Trainers can be found.
Wild Pokemon:
Surfing (Levels 27-30): Finneon(40%), Tentacool(40%), Pelipper(20%)
Fishing (Levels 10-30): Magikarp(79%), Wishiwashi(20%), Bruxish(1%)
SOS Pokemon #1 (Levels 10-30): Gyarados, Wishiwashi, Bruxish
SOS Pokemon #2 (Levels 10-30): Magikarp, Wishiwashi, Bruxish
Fishing Bubble Spots (Levels 10-30): Magikarp(50%), Wishiwashi(30%), Bruxish(20%)
SOS Pokemon #1 (Levels 10-30): Gyarados, Wishiwashi, Bruxish
Berry Trees (Levels 27-30): Crabrawler(100%)
Zygarde Cells: There are two Zygarde Cells found here.
Trainers:
Swimmer Sara - Level 30 Alomomola
Swimmer Robert - Level 29 Whiscash, Level 30 Sandygast
Items:
Leppa Berry - Berry Tree
Cheri Berry - Berry Tree
Aspear Berry - Berry Tree
Chesto Berry - Berry Tree
Apicot Berry - Berry Tree
Pearl - West of Berry Tree (Hidden)
Big Pearl - Between Slowpoke (Hidden)
Pearl - Near Swimmer (Hidden)
Big Pearl - Near Rock South of Swimmer (Hidden)