Walkthrough: In order to get to Po Town, you must start of Route 15 and head north. Luckily, the Unova Elite Four Member Grimsley will help with giving you the Sharpedo Poke Ride.
Wild Pokemon:
Grasses - Daytime (Levels 30-33): Pelipper(50%), Gumshoos(30%), Slowpoke(20%)
Grasses - Nighttime (Levels 30-33): Pelipper(50%), Raticate(30%), Slowpoke(20%)
Surfing (Level 30-33): Finneon(40%), Tentacool(40%), Pelipper(20%)
Fishing (Levels 10-33): Magikarp(79%), Wishiwashi(20%), Bruxish(1%)
SOS Pokemon #1 (Levels 10-33): Gyarados, Wishiwashi, Bruxish
SOS Pokemon #2 (Levels 10-33): Magikarp, Wishiwashi, Bruxish
Fishing Bubble Spots (Levels 10-33): Magikarp(50%), Wishiwashi(30%), Bruxish(20%)
SOS Pokemon #1 (Levels 10-33): Gyarados, Chinchou, Wishiwashi
Zygarde Cells: There is one Zygarde Cell found here.
Trainers:
Ace Trainer Yuki - Level 32 Sandshrew, Level 33 Marowak
Swimmer Jared - Level 33 Tentacruel
Ace Trainer Karla - Level 34 Vulpix, Level 34 Haunter, Level 35 Wigglytuff
Swimmer Yumi - Level 33 Slowbro
Swimmer Jake - Level 33 Golduck
Swimmer Alexandria - Level 33 Luvdisc, Level 33 Corsola, Level 33 Alomomola
Trial Guide Katrina - Level 34 Klefki, Level 34 Skarmory
Items:
TM93 Wild Charge - Blank Island
Luxury Balls x5 - From Lillie
Stardust - In Rock In Southwest Ocean
Dive Ball - Beach North of Swimmers Yuki & Jake
Hyper Potion - North of Ace Trainer Karla
PP Max - Defeat Trial Guide Katrina
Pearl - North of Fisherman (Hidden)
Normal Gem - North Beach (Hidden)