After leaving Mossdeep, the route proceeds to the southwest, passing three shallow areas of the route containing an item and a Trainer. East of the second island in this group, the main underwater cavern begins, allowing Trainers to use Dive to head to the ocean floor. To the south of the second island is a large rock formation that splits the route into two north-south paths. The west path connects to a channel that leads to Route 126 and Sootopolis City before merging with the east path.
Northeast of this point is a large island holding three Trainers. To the south of the island is a lone Swimmer. South of the Trainer is another large island, holding a single Trainer. Off the northeastern shore of the island is a deep spot in the ocean, which leads to a small underwater passage that ends just north of the starting point. After reemerging on the surface, Trainers can Surf to the northwest to land on a shallow island populated with trees and a Carbos.
Returning to the main path, the route passes by another Swimmer before becoming Route 128.
Changes in Emerald
In Pokémon Emerald, the third island in the northwest corner became populated with trees and became the location of a Rare Candy. Another Trainer was added to the island as well.
Entrances to the Marine Cave were also added underwater.
All items on Route 127 can only be accessed with the use of Surf.