Crater Edge

The Dead Zone borders the entire map of Subnautica. It is the area beyond the crater of an enormous, dormant, aquatic volcano, which is where Subnautica takes place.

The Dead Zone is the end of the map and has a small amount of unfinished terrain at 3000 meters depth. Past that terrain there is another, seemingly infinite drop. After ~8000 meters depth, the player teleports back to Lifepod 5.

Multiple adult Ghost Leviathans live in the Dead Zone, where they act as a deterrent for wandering players going outside of the playable area.

In fact, the Dead Zone (Void) biome is not infinite, it has a circle form, that goes up to 3800-4000 meters away from map center. Crossing the border of this zone - you left the dead zone biome and entering no biome zone. All ghost leviathans, that chase you in the Void will turn back and left you in no biome zone. You can even reach it in survival, using cyclops, seamoth and seaglide with stasis rifle (Guaranteed way).

Also the game would not teleport you back to Lifepod 5 until you reach the 8000 meters depth, it doesn't count the far distance from 0/0/0 coordinates, only depth.

Description
True to its name, the Dead Zone is a large open ocean devoid of any flora, coral, and all but one fauna species.

Fauna

 * Ghost Leviathan

Trivia

 * Sea Dragon Leviathans, Reaper Leviathans, and other fauna, were planned to spawn in the Dead Zone at one point, but this idea was scrapped.
 * The Dead Zone was originally called The Void.
 * The Dead Zone is the deepest biome in the game.