Including rules for underwater combat and how to optimise for aquatic adventures.
A slimy tentacle grasps your ally by the leg, dragging them off the boat and into the murky water. Without hesitation, you dive into the water, weapon ready to severe the tentacle and rescue your friend…
Exciting start to a combat encounter, but aquatic combat doesn’t often come up. Because of this, these rules often get forgotten by players and DMs, leading to a scramble through the rulebooks to understand how it works, leaving everyone on the backfoot.
This is made worse by the fact that the rulebooks tend to have the rules in separate locations, leading to a merry chase between the Player’s Handbook (PHB) and the Dungeon Master’s Guide (DMG).
This guide is here to help bring all that information into one place so you can easily find all the rules you need to know. I’ll be sharing references to the relevant rulebooks so you can check any specific wording you need o. I’ll also cover off any differences between the 2014 and 2024 editions of D&D 5e so it doesn’t matter which edition you’re using, this guide will still give you what you need to know.
Rules at a glance
If you just need a reminder of the core rules of swimming and being underwater, I’ve summarised them here. I’d still suggest reading all the details later as there’s more to it than this, but these are the basics and will help you get by if you’re just looking these up mid-encounter.
- Swimming costs an extra foot of movement unless you have a swim speed.
- You can hold your breathe for 1 + con modifier minutes. After this, you begin to suffocate.
- Melee weapons have disadvantage underwater unless you’re using a dagger, javelin, shortsword, spear or trident in the 2014 rules or a piercing weapon in the 2024 rules.
- Ranged weapons always miss when shot at long range.
- All ranged weapons in the 2024 rules have disadvantage underwater. In the 2014 rules, crossbows and thrown weapons don’t have disadvantage underwater.
- The distance you can see underwater is reduced depending on the light and murkiness of the water, ranging from 10-60ft. You also have disadvantage on perception checks underwater.
How does swimming work?
Movement while swimming
PHB 2014 – p182
PHB 2024 – p376
Your movement speed when swimming is worked out by using your movement speed, except that every foot of movement costs 1 extra foot. So if you want to swim 10ft, it’ll cost you 20ft of movement. This means that many characters with a 30ft movement speed will only be able to swim 15ft on their turn.
You can still do things like dash with the same rules applying, so a creature that dashes while swimming with a 30ft movement speed will get 60ft of movement, but because of the extra cost for moving while swimming, the furthest you can swim is 30ft.
Some characters and creatures have a swim speed, in which case, this overrides the extra movement cost and you can simply move as far as your swim speed states.
If swimming in rough water, your DM might request a DC15 athletics check to be able to move at all.
Swimming and exhaustion
DMG 2014: p116
2024: I couldn’t find any reference to mechanics for exhaustion during prolonged swimming in the 2024 rules.
Swimming is much more tiring than walking (unless you happen to be an octopus). When a character swims for an hour, they must take a constitution saving throw (DC10) or gain a level of exhaustion. The DMG also states that no one can swim longer than 8hrs unless they have a swim speed. Creatures with swim speeds are also exempt from any penalties from the hourly exhaustion saving throws, but do still need to use the rules for forced marching.
This simply means you can travel as normal for 8hrs a day, but for every hour you travel beyond this, you risk gaining levels of exhaustion.
Swimming deep underwater
DMG 2014: p116
Note: Again, the 2024 rules don’t provide specifics on rules for deep swimming.
Swimming deep underwater is harder than swimming higher up due to the pressure. As such, if you don’t have a swim speed, swimming 100ft below the surface will cause 1hr of swimming to count as 2hrs when calculating exhaustion.
Once you get 200ft below the surface, each hour swum will count as 4hrs for calculating exhaustion. All of this assumes you can find a way to hold you breathe long enough to do this.
How does being underwater work?
Holding your breathe
PHB 2014 – p183
PHB 2024 – p376
You can hold your breath for 1 + constitution modifier minutes. Once you can’t hold your breath any longer, you begin suffocating. In the 2014 rules, this drops you to 0HP and you begin dying. You will die in a number of rounds equal to your constitution modifier unless you reach air. In the 2024 rules, you’ll gain a level of exhaustion at the end of each turn you’re suffocating, losing all levels of exhaustion caused by suffocating once you stop suffocating.
Combat underwater
Weapon attacks underwater
PHB 2014 – p198
PHB 2024 – p27
Fighting underwater is obviously more challenging than fighting on land. Because of this, weapon attacks are often less effective.
- Melee weapon attacks have disadvantage unless you’re wielding a dagger, javelin, shortsword, spear or trident. This list of weapons is expanded in the 2024 rules to include all piercing weapons which means the likes of lances, rapiers and morningstars don’t have disadvantage underwater either.
- However, characters with a swim speed don’t have disadvantage on melee attacks no matter the weapon.
- Ranged weapons have disadvantage underwater unless you’re using a crossbow or a thrown weapon in the 2014 rules. In the 2024 rules, all ranged weapons have disadvantage underwater.
- Also, all ranged weapons automatically miss when fired at long range.
Spellcasting underwater
PHB 2014: p198
PHB 2024: p27
Jeremy Crawford (lead designer)
Spells are cast as normal underwater and spell attacks don’t receive disadvantage. However, as mentioned before, casting spells requiring verbal components will cause you to stop holding your breath.
Its also worth being aware that any creature completely underwater has resistance to fire damage.
Seeing underwater
DMG 2014: p117
DMG 2024: p36
Seeing underwater is much harder, as such, visibility is impaired unless you have a light source (note that the 2024 rules don’t differentiate between having a light source for underwater visibility). When underwater, you can see at these distances with the following brightness:
- Murky water or no light – 10ft
- Clear water and dim light – 30ft
- Clear water and bright light – 60ft
Perception check in dim light will roll with disadvantage, even if you have darkvision.
Optimising for swimming and being underwater
If you’re expecting to be in water a lot, you may want to build around swimming and underwater combat. Here’s a bunch of options you can use to help here:
- Gain a swim speed – Some species and classes gain a swim speed. This includes the likes of Sea Elves, Water Genasi, Giff, Lizardfolk, Locathah, Simic Hybrid and Triton. Rangers and circle of the sea druids also gain a swim speed at level 6.
- Be able to breath underwater/hold your breath longer/don’t need to breath – This will help you last longer underwater. Several races have these benefits including; Sea Elf, Air Genasi, Water Genasi, Autognome, Dhampir (but only the 2014 version), Grung, Lizardfolk, Locathah, Plasmoid, Simic Hybrid, Tortle, Triton, Vedalken and Warforged.
- Wield piercing weapons – If you’re using the 2014 rules, these weapons are a little more limited, but it’s always a good idea to carry a dagger or 2 on you just in case you fall in some water.
- Use spells – Some spells can help you gain some of these abilities. This includes the likes of alter self, water breathing and water walk.
- Get a mount that can swim – If you don’t have a swim speed, you can always grab a mount that does. A beastmaster ranger can gain a companion that can do this or you could befriend or summon a creature like this.
- Transform into a creature that’s good in the water – Druids with wild shape can do this. Alternatively, you can use things like the polymorph spell to transform into an aquatic creature.
- Use non-verbal spells – If you attempt a verbal spell (unless you don’t need to breath or can breath underwater) then you’re going to get into loads of trouble. You’re better off making sure you have at least a few spells you can use underwater that don’t require verbal components.
That’s everything you need to know about how swimming and being underwater works in D&D 5e.
