Swimming Speed

Swimming Speed determines how fast the player moves in water. As of around October 2022 the swimming speeds in both Subnautica and Subnautica: Below Zero are the same.

The swim speed can be affected by: whether or not you swim underwater or on the surface, the suit(but not mask or gloves), oxygen tank, fins, holding tools and whether or not you have additional oxygen tanks in the inventory.

The base swim speed is 5.75m/s under water and 6.14m/s on the surface. With a Seaglide, the base value is 11m/s underwater and it doesn't work on the surface at all. The game then applies modifiers to these values:

Effects on Swimming Speed (in meters per second)
Modifier	Underwater (m/s)	Surface (m/s)
Fins	+1.41	+1.85
Ultra Glide Fins	+2.38	+3.12
Swim Charge Fins	0.00	0.00
Standard 02 Tank	-0.32	-0.42
High Capacity O2 Tank	-0.37	-0.50
Ultra High Capacity O2 Tank	-0.48	-0.62
Lightweight High Capacity Tank(Subnautica)	-0.08	-0.10
Booster Tank(Below Zero)	-0.37	-0.50
Booster Tank Boost(Below Zero)	+2.16	n/a
Holding a Tool	-0.75	-0.97
Reinforced Dive Suit	-0.75	-0.97
Seaglide
Fins(any type)	0.00	n/a
Standard O2 Tank	-0.05	n/a
High Capacity O2 Tank	-0.10	n/a
Ultra High Capacity O2 Tank	-0.20	n/a
Lightweight High Capacity Tank(Subnautica)	0.00	n/a
Booster Tank(Below Zero)	-0.10	n/a
Booster Tank Boost(Below Zero)	+1.87	n/a

Additional notes:

• The values may be off by 0.01-0.02 because the values displayed are rounded to 0.01
• Reinforced Dive Suit is the only suit with a speed penalty; Reinforced Gloves have no penalty and still provide 10% damage resistance
• Ultra High Capacity Oxygen Tank has a speed penalty when you carry it in the inventory; all other tanks have no such effect
• Seaglide does not benefit from the fins at all but you can still use Swim Charge Fins to charge it as you go