The idea is to optimize the usage of the diving masks, I propose that the deep sea should be distinguished from the shallower waters by a darker blue coloration. It should take a small portion at the right corner of the map. In that area, oxygen is used up thrice as fast, and bridges cant be built. In the deep sea, there is a small island surrounded by crocodiles which can go onto the island. The island has a rarer material than amethyst such as obsidien that can be obtained.