From the Super Mario Wiki
Crescent Coast is the fourth level in the game Yoshi's Safari. As the name implies, it takes place on a crescent shaped coast. Crescent Coast is located on the south end in the Light Realm of Jewelry Land. The beginning of the level consists of a sandy beach that Mario and Yoshi must traverse. Mario and Yoshi will eventually reach the end of the beach and get into the water. Then, the whole level changes to an underwater exploration level.