Answer: When that floating island is a gigantic polyurethane balloon filled with helium. It's an art project called Is Land and has trees and foliage decorating it to make it seem like a floating island. But it's gone!
Eat your heart out, Dubai—the world's largest floating island has just opened in Seoul, South Korea, where it'll be joined by several other artificial islands to become an archipelago.
The Maldives, a small nation consisting of 1,200 islands is gradually disappearing as sea levels rise. In an attempt to save the place, their government has signed off on the development of several "floating facilities" like this one.