After reaching John Waals' House in Chapter 4 of the game, you will learn that Brad is there trying to arrest Mr. Waals, claiming he is the culprit for the mysterious fog happening at the Lake found within the Island. In order to prove John Waals' innocence, Tim and Pikachu (along with Milo) must head to the lake and prove otherwise. Unfortunately, the bridge to the lake is presently broken, which forces Tim and Pikachu to Find an alternate route.
After talking with the various people on the Island, you will learn that there is a Secret Path to the Lake located somewhere on the island. If you continue to investigate, you will learn that there use to be scrolls given to the children of the island long ago in order for them to Find the secret path to the lake. Going off of one hint you will receive, you will be able to obtain one of these scrolls from the old man that lives in one of the houses near John Waals' Home.
After receiving the Scroll, you will need to Find the entrance to the Secret Path. The old man you received the scroll from will inform you that the secret path begins with the scales, not being able to explain where you can find said scales. However, by examining the broken rocks to the right of Waal's House, you will see two scales engraved in one of the stones. This is the beginning to the secret path, the same Milo will ask to travel with you after you discover it.
Once you enter the Secret Path, you will examine the Scroll you received. There will be a lot of information found on the scroll, but the only thing you will really need are the colors that are shown. To Find the first path, you will need to Match the statue to the color green. Since Tropius is covered in green leaves across its body, you will need to take its corresponding path. After taking this path, you will have to make it through the path full of Stunfisk with Pikachu, which just so happens is your next Fast Action Event.
After making your way through the Stunfisk, you will arrive to the next set of statues. Unfortunately, the colors of these statues have faded. In order to Find the correct Path, you will need to find the Pokemon that is originally blue. Out of all the Pokemon shown in the form of statues, Ducklett is the only one that is the color blue. Take the path connected to the Ducklett Statue to arrive to the third and final area before the Lake.
When you reach the third area, you will need to Find the statue of the Pokemon that is pink, like shown on the Scroll. Unfortunately, none of the Pokemon are pink. You might think this is a mistake at first, but after doing some investigating, you will discover that Shellos can be found in one of two different forms, one of which is the color pink. By following the Path near the Shellos Statue, you will finally arrive at Lake Cappucci.