Part of the Exploration & Endgame series:

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Planet Types, Biomes & Hazards: Finding water worlds.

Quick Answer

Underwater survival runs on a separate oxygen stat, not your normal life support or hazard protection. Once it empties you start drowning.
Oxygen underwater is extended by exosuit upgrades, the Aeration Membrane being the standard first purchase, with stacking upgrade modules beyond that.
The Nautilon is the submarine exocraft. It is built from its own geobay, carries its own mining laser and scanner, and removes the oxygen problem entirely while you are inside it.
Bases can be built on the sea floor, and the build menu includes dedicated underwater rooms and corridors that keep water out.
The reward for going down is real: aquatic-only fauna that count toward a planet's creature catalogue, sunken and abyssal structures, resources that do not appear on land, and fishing spots.
Worlds Part I overhauled water rendering and ocean depth, which is why full ocean planets became somewhere worth spending a session rather than somewhere you flew over.

Overview

Water in No Man's Sky used to be scenery. You swam out far enough to spook yourself, watched the oxygen bar drain, and turned back. Since the water and terrain overhaul in Worlds Part I, oceans got deeper, clearer, and more varied, and planets that are almost entirely ocean became a legitimate destination rather than a rendering curiosity.

The change matters because a substantial slice of some planets' content sits below the waterline. Creatures that never surface still count toward the catalogue. Structures sit on the sea floor. Certain plants and minerals grow nowhere else. If you are surveying a water world and only walking its islands, you are surveying a fraction of it.

Going down properly needs three things: enough oxygen to survive the trip, a way to cover distance, and somewhere to work from. This guide handles all three.

Surviving Underwater

Underwater is its own hazard category. It does not share a meter with cold, heat, toxicity, or radiation, and hazard protection upgrades do nothing for it. What you have instead is a dedicated oxygen supply that begins draining the moment you submerge.

Two things follow from that. First, a fully upgraded hazard build can still drown, which surprises players who assume their survivability is universal. Second, oxygen underwater is fixed by exosuit technology specifically, not by anything you install on your ship or multi-tool.

Underwater hazard	What it actually does	Response
Oxygen drain	Separate stat, empties on a timer while submerged	Aeration Membrane, then stacking oxygen upgrade modules
Drowning	Health loss once oxygen is gone	Surface immediately, or enter the Nautilon
Aquatic predators	Aggressive fish and larger creatures attack while you swim	Move to open water, use the Nautilon, or leave the area
Distance	Swimming is slow and eats oxygen you cannot spare	Nautilon for anything beyond a short dive
Darkness at depth	Poor visibility hides both terrain and threats	Exocraft headlights, base lighting near your work site

The Aeration Membrane is the exosuit technology that extends underwater breathing, and it is the baseline for anyone diving on purpose. Further oxygen upgrades stack on top of it, and installing them close together in your exosuit's technology slots follows the same adjacency logic as the rest of your loadout.

There is a simpler trick that carries you a long way early on: pockets of air. Underwater base structures hold breathable atmosphere, so a single sealed room dropped near a dive site works as a refill station. So does surfacing, which is free but slow if you are working at depth.

For the wider survival picture, including how the underwater meter fits alongside the hazard and life support systems you already manage, our survival and life support guide covers the full set.

The Nautilon Submarine

The Nautilon is the exocraft built for underwater travel, and it changes the activity completely. Inside it, oxygen stops being a consideration. You are in a sealed vehicle, so a dive becomes a drive, and the sea floor becomes traversable rather than something you glimpse before turning back.

Like every other exocraft, it needs its own summoning point. The Nautilon Chamber is its geobay, built at a base, and it is placed underwater rather than on land. Once you have one, the Nautilon can be summoned in the usual way for exocraft.

Nautilon feature	Why it matters below the surface
Sealed cockpit	No oxygen drain at all while you are aboard
Mining laser	Harvest sea floor resources without exiting the vehicle
Scanner	Locates points of interest underwater the way other exocraft scanners work on land
Speed	Covers ocean distances that swimming makes impractical
Storage	Somewhere to put what you gather on a long dive

The scanner is the part players underuse. Sweeping the sea floor from a moving submarine is how you find structures and resource concentrations you would otherwise never happen across, and it is far faster than swimming a grid pattern with an eye on your oxygen bar.

The Nautilon's blueprint and construction sit within the same exocraft progression as the Roamer, Colossus, and the rest. If you have not built exocraft before, or you want the full picture on geobays, upgrades, and summoning, see the exocraft guide.

The Nautilon is a vehicle, not a bunker. Getting out at depth puts you back on your own oxygen supply, so plan exits around where you can resurface or reach a sealed room.

Building Bases Underwater

Sea floor bases are fully supported, and the build menu contains parts made for it. Underwater rooms and corridors seal against water, hold atmosphere, and connect the same way their surface equivalents do. A small submerged outpost is one of the cheapest quality-of-life investments in the game if you are working an ocean world.

What an underwater base gives you:

Function	Practical benefit
Breathable interior	A refill point that removes the swim back to the surface
Nautilon Chamber	A summon point for the submarine at your actual work site
Storage and refiners	Process sea floor material without a return trip to orbit
Teleporter	Direct arrival at depth instead of a descent every session
Landing pad above	Ship access on the surface, linked to the base below

Placement matters more underwater than on land. Flat sea floor near the features you actually care about beats a scenic spot with nothing around it. If you plan to build seriously below the waterline, the base building hub covers the structural rules, power, and boundary limits that apply the same way whether you are wet or dry.

What Is Actually Down There

The reason to invest in any of the above is what the ocean holds.

Aquatic fauna. A meaningful chunk of a planet's creature catalogue can live entirely underwater, and those species never surface. Completing a planet's discovery record on a water world means diving for it. Some of the rarer species in the game are aquatic, which is why serious cataloguers treat oceans as priority terrain rather than filler. Our rare creatures and discovery guide goes into how to track down the species that hide from casual scanning.

Sunken and abyssal structures. The sea floor holds its own points of interest, including drowned buildings and crashed sites that do not appear on land. These are located by scanning, which is where the Nautilon's scanner earns its place.

Resources with no land equivalent. Certain plants and minerals grow only in water, and harvesting them requires either a dive or a submarine with its mining laser. For anyone running refining or crafting chains, this is a supply line that surface players never touch.

Fishing spots. Fishing added an entire secondary activity to bodies of water, with catches that vary by planet, biome, and time of day. It runs from the surface rather than from depth, but it is part of the same reason to seek out water worlds. The fishing guide covers rigs, bait, and what determines a good spot.

Sea floor excavation. Fossil dig sites appear underwater as well as on land, which is another case where the Nautilon turns a tedious swim into a short drive.

Challenges and Solutions

Challenge	What solves it
Oxygen runs out too fast	Aeration Membrane plus stacked oxygen upgrades in adjacent exosuit tech slots
Swimming is too slow to explore	Build the Nautilon Chamber and use the submarine
Nothing visible on the sea floor	Scan from the Nautilon rather than searching by eye
Predators interrupt every dive	Stay in the submarine, or relocate away from the aggressive population
Long trips back to the surface	Drop a small sealed underwater base with a teleporter
Can't find a real ocean planet	Survey water-heavy worlds since the Worlds Part I overhaul; check systems from orbit before landing
Missing creatures in the catalogue	Assume the gaps are aquatic and dive with the Analysis Visor ready
Cargo full mid-dive	Use Nautilon storage, or build a base container near the site

FAQ

How do I breathe underwater longer?

Install the Aeration Membrane on your exosuit, then add oxygen upgrade modules on top of it. Underwater oxygen is its own stat, separate from life support and hazard protection, so general survivability upgrades will not help. Sealed underwater base rooms also refill you without surfacing.

How do I get the Nautilon?

Build its geobay, the Nautilon Chamber, at a base and summon the submarine from it. It follows the same acquire-blueprint, build-geobay, summon pattern as the land exocraft, with the difference that the chamber goes underwater.

Can I build a base underwater?

Yes. Bases can be placed on the sea floor, and the build menu includes underwater-specific rooms and corridors that hold breathable atmosphere. Everything else you would normally install, including storage, refiners, and teleporters, works below the waterline.

What is worth finding underwater?

Aquatic-only creatures that count toward the planet catalogue, sunken structures and crashed sites, plants and minerals that do not grow on land, fossil dig sites, and fishing spots. On a genuine ocean world this is most of the planet's content.

Do aquatic creatures count toward planet completion?

Yes. Species that live entirely underwater are part of the same discovery catalogue as surface fauna. A planet you have "fully" scanned from land is often incomplete for exactly this reason.

Key Takeaways

The ocean is the part of No Man's Sky most players still treat as background. That was a reasonable habit before Worlds Part I, when water was shallow, murky, and mostly decorative. It is a bad habit now. Deeper, more legible oceans mean water worlds have terrain, structures, and populations worth the trip.

The gear ladder is short. Aeration Membrane and a couple of oxygen modules make short dives comfortable. The Nautilon and its chamber make long ones trivial. A single sealed room on the sea floor turns an ocean into a workspace. None of that is expensive by mid-game standards, and all of it is reusable across every water world you visit afterwards.

What you get back is the half of a planet you were skipping. Catalogue entries you could not otherwise complete, resources with no surface equivalent, structures nobody walking the beach will ever see, and fishing on top of it. Treat the waterline as a border you cross rather than a ceiling, and ocean planets stop being the ones you fly past.

No Man's Sky Underwater Guide: Nautilon, Ocean Bases & Deep-Sea Survival