Well, well, it's time to step back into the sea. There are slightly less Diglett compared to Workout Sea, so this should be less of a workout. However, there's still plenty of sea after you're done with this zone, so don't relax just yet!
1/7: Start from the Tower of Waters in Challenge Beach. Go to the left of the tower (while facing the tower entrance) and face the ocean. There should be an elongated pair of islands straight ahead. To the right is another island, with two trees. Swim to the second island. Upon arrival, turn right from the shore. The first one's on the right side of the red flowerbed in front of the berry tree.
2/7: From Diglett 1, approach the nearby big tree. The second one's by the edge of the land, next to some pebbles, to the right of the tree.
3/7: From Diglett 2, turn around and head for the opposite end of the island, where the second tree is, past the tall grass. It's next to some pebbles above the red flowerbed to the left of the tree.
4/7: From Diglett 3, head back towards the shore, but turn right while facing the ocean/mainland. Head into the narrow path, where the Pokémon Den is. The final Diglett on this island is at the end of this path, near the gold item ball.
5/7 and 5/6: From the island where Diglett 1~4 are, head for the shore and face the elongated pair of islands (on the right, if you're facing the mainland). To the left of the pair of islands is an islet that has a boulder (it might look like a blob from here). Swim to the islet. Search to the left of the boulder to find two Diglett.
7/7: From the islet where Diglett 5 and 6 are, turn so the mainland is on your left. Directly, there's a long, sandy island with a boulder on one end and a Pokémon Den on the other. Swim towards that island. Check around the middle of this island.
The number of rescued Diglett should be exactly 130 now. You'll get no reward this time, but you can have a pat on the back from us!