Around the middle of the route, you can use Surf to ride on the water. Follow the watery path until you reach the shoreline.
Just to the west of the shore is a Full Restore yours for the taking. Head up the stairs to the east and you'll find an Ace Trainer wandering around. He has a Durant L66, an Espeon L66, and a Honchkrow L66. South of him is another Ace Trainer. She uses a Heatmor L66, an Umbreon L66, and a Mismagius L66. There's also a hidden Protein right near her, too.
Southwest of them is a PKMN Ranger, who uses a Wigglytuff L64, a Girafarig L64, and a Vileplume L64 on her team. Beat her and she'll give you a Lum Berry for your efforts. To the east of her is yet another PKMN Ranger, except this guy has a Vigoroth L64, a Stantler L64, and a Victreebel L64. He, too, will give you a Lum Berry after your victory. Just past him is a Prism Scale, which can be held by a Feebas to evolve it when you trade it.
Now make your way over to the gate to the west to reach Route 17!