Swamp

Lore & Background

In the broader Oxygen Not Included world, the Swamp occupies a liminal space between the open sky and the deep rock below. It is a biome of transition—where rainwater has pooled, where organic matter has settled into thick, dark mud, and where the thin line between fertile and foul is constantly blurred. The Duplicants who first arrive in a colony seeded above or beside a Swamp quickly learn that what looks like a quiet, green landscape is actually a slow, patient machine for spreading contamination.

The Swamp's ecology is simple but insidious. Grass grows in tufts along the mud's edges, wood accumulates in the shallows, and the water itself carries a persistent taint that seeps into anything it touches. There is no dramatic monster lurking in the reeds; the danger is chemical and gradual. A single puddle of dirty water left unmanaged can taint a clean-water pipe, and a pipe left unmanaged can poison a Duplicant's oxygen supply. The Swamp does not attack. It simply waits for you to get careless.

Among the fan community, the Swamp has earned a fond reputation as the "tutorial biome with teeth." It teaches the core loop of the game—harvest, process, manage, repeat—without the lethal pressure of the deeper biomes. Many players remember their first Swamp colony with a mix of affection and mild trauma, a small green-and-brown cross-section where everything seemed manageable until the water table shifted and everything was not.

In Their Own Story

The morning shift Duplicant found the mud had crept two tiles further into the kitchen. She knelt, pressed her palm flat against the cold, slick surface, and felt it give a slow, wet sigh. Outside the porthole, the Swamp stretched in its endless grey-green murmur—grass bending in a breeze that smelled of iron and rot, the dirty water lapping at the foundation with the patience of something that had been here long before the colony and would be here long after.

She pulled up her tablet. Water pressure nominal. Oxygen at 99.8 percent. All green. All fine. She looked back at the mud, then at the clean-water line running just above it, and felt the particular stomach-drop that meant the Swamp was winning by a margin no dashboard could yet show. She grabbed a shovel. The reeds swayed. The water kept lapping. It had all the time in the world.

Reader's Guide

The Swamp occupies the upper cross-section, typically within the first 10–15 tiles below the surface. Its temperature hovers around 20 °C, well within the comfortable range for Duplicants, and the atmosphere is a standard oxygen-nitrogen mix, so no special gear is needed for basic work.

Key tiles you will encounter: dirty water (the dominant liquid, which must be pumped and filtered before use), mud (a soft solid that can be dug but also spreads contamination to adjacent clean tiles), grass (a renewable organic resource usable in composting or as fuel), and wood (a solid building material found in the shallows and along the mud's edges). Stone and basic minerals may appear in the lower layers of the Swamp.

The primary hazard is contamination. Dirty water does not evaporate or neutralise on its own; it seeps, pools, and tints any clean water it contacts. A single unmanaged leak can cascade through a water network. Mud, while diggable, is slippery in practice—Duplicants working in it will move slower, and the soft ground can undermine foundations if not reinforced.

Practical tips: build your water-processing station (filter + pump) before you expand into the Swamp's lower tiles. Keep a margin of at least two solid tiles between any dirty-water pocket and your clean-water infrastructure. Harvest grass and wood early; they are cheap, renewable, and will be in demand once you move to deeper biomes. And always check the water table after rain events, because the Swamp's water level is not fixed.

Did You Know?

• The Swamp's dirty water is one of the few liquids in the game that actively contaminates clean water on contact, making it a persistent management challenge rather than a one-time cleanup.
• Grass in the Swamp is a renewable resource—once cut, it regrows over time, making the biome a reliable long-term source of organic material for composting and fuel.
• Because the Swamp sits at the surface with a standard atmosphere, it is one of the safest biomes for new Duplicants to work in, with no toxic gas or extreme temperature risks.
• The Swamp's mud behaves differently from solid rock: it can be dug, but it also creates a soft, slow-moving surface that affects Duplicant movement speed and can undermine nearby structures if left unmanaged.