You can get this small island from the Chaweng beach. The ocean is shallow here (the depth is no more than 1 meter), so you can walk across. Water shoes will be a good option here! A way to the statue is not visible from the beach, so you just need to enter 10 meters inside the jungles.
After you find the cache you can go down to the ocean - there is a place for instagrammable selfies ;)