Imagine if this island initially was submerged in the deep sea and after unlocking a secret from a gate or something else. It would raise up to be revealed in the sea the Area 3834 Secret market island.
This secret location brings many for black market sales not found around local parts and purchases also to do specialist fishing and relax.
The island is powered by fishes headbutting each other, fish poop /oil. sea waves, storms and even electric eels living inside the lower level of the island itself!
When the island needs to vanish back into the depths of the sea uses seaweed camoflauge while powering down to reduce it's location signature!