Underwater Combat in D&D 5e
While individual combat encounters in D&D 5e are dynamic and ever-changing, the rules that govern these encounters thankfully don’t change much. One of the few scenarios where some additional rules come into play is underwater combat encounters.
Depending on the campaign or adventure module you’re playing, you may never find yourself fighting throngs of enemies below sea level. On the other hand, it’s not outside of the realm of possibility for an underwater combat encounter to come into play. Even if you hadn’t intended there to be underwater combat when planning the encounter.
Regardless, thankfully the underwater combat rules in 5th edition are pretty easy to remember. The majority of the rules revolve around limiting the effectiveness of certain types of weapons and spells. Realistically, this makes sense. For example, it’s more difficult to swing a sword or shoot a bow underwater.
First of all, moving underwater is difficult terrain. While this isn’t technically tied into the underwater combat rules, it’s a significant point to remember when running an underwater encounter.
Difficult terrain just means that characters and creatures move at half speed unless otherwise noted. For example, difficult terrain as far as swimming underwater is concerned can be ignored if your character or creature has any amount of swim speed.
You could gain swim speed as a racial trait from races like tritons or sea elves do. Some classes and archetypes may also grant swimming speed such as the Path of the Storm Herald Barbarian. Another, more accessible option, is to obtain a magical item that grants the user swim speed.
Understandably, not all weapons are able to work effectively underwater. The list of what weapons do work is pretty small so at least it’s easy to remember what will and will not be detrimental to use underwater.
If you’re using aquatic creatures like merrow as the DM you won’t have to worry about weapon disadvantages. I’ve found that most aquatic creatures use weaponry that isn’t hindered by being underwater.
Melee Weapon Restrictions
Melee weapon attacks are made at disadvantage by creatures underwater. However, there are a few exceptions to this rule. If you are using a dagger, javelin, shortsword, spear, or trident you can make a regular weapon attack.
Notice that all of these are piercing weapons, weapons that are thrust straightforward when attacking. This makes practical sense too, there’s less resistance from the water when thrusting as opposed to swinging a slashing or bludgeoning weapon.
Having swim speed is a huge boon to any melee attackers. This isn’t just because of the increased speed and maneuverability, though. It’s also because having a swimming speed means that you can use any melee weapon without having disadvantage on the attack roll.
I’m assuming that the logic behind this is that you’re clearly an expert at swimming so you’ll know how to swing a sword with enough power and accuracy to reliably deal damage.
To remember this simply determine if the melee weapon is a piercing weapon you thrust forward with. If it isn’t then you have disadvantage on the attack unless you have any swim speed.
Ranged Weapon Restrictions
As you might imagine, shooting a longbow is terribly difficult underwater. Not only that but even if you managed to pull the bowstring back the resistance from the water would slow the arrow making it extremely inaccurate.
Ranged attacks are made at disadvantage unless the weapon is a crossbow, net, or a weapon that is thrown like a javelin such as a spear, trident or dart. Essentially, ranged weapons that are manually drawn like bows or thrown in a swinging motion like a handaxe will make their attacks at disadvantage.
In addition to this, any ranged weapon attack must be within the weapon’s normal range otherwise it automatically misses. This means that a heavy crossbow can only be shot within 100 ft. underwater even though it has a maximum range of 400 ft.
Firearms and explosives typically don’t work underwater, though that may depend more on your setting than anything. Most of the firearms I implement in my games use powder to fire. It’s hard to do that when the powder is wet!
The only real benefit to underwater combat in 5e is that everyone who is fully submerged in water has resistance to fire damage. Even then, it’s not much of a benefit for the players from my experience.
Figure it this way, most creatures that the party will be fighting underwater are probably aquatic or have spent a lot of time in or around the water. Their statblocks, abilities, and spells generally don’t include fire damage.
Fire damage is found in some signature spells like fire bolt, burning hands, and fireball which most offensive wizards or sorcerers have at least one of. Reducing the effectiveness of these lessens the party’s damage output.
Typically these mechanics breakdown articles are a lot lengthier, but underwater combat isn’t very challenging to interpret. I’d go as far to say that the vast majority of the rules for underwater combat can be assumed by thinking logically about the situation.
- Ranged weapon attacks are at disadvantage
- Unless the weapon is a crossbow, a net, or a weapon that is thrown like a javelin
- Ranged weapons automatically miss if they are attacking a target outside of the weapon’s normal range
- Melee weapon attacks are at disadvantage
- Unless the weapon is a dagger, javelin, shortsword, spear, or trident
- Unless the attacker has swim speed
- All creatures submerged in water have fire resistance
Underwater combat is restrictive, but it’s certainly not detrimental, even to creatures without swim speed. It opens up some unique maneuvers as it’s also three-dimensional combat. Enemies and allies can be above and below you at all times now which is not typically the case when fighting on flat land.
Underwater movement is NOT ‘difficult terrain’. Underwater movement halves your movement speed (check the PHB) unless you have a swim speed. That may sound like the exact same thing, but this is an important distinction — as there are things like the Mobile feat that say in some condition or other ‘you ignore difficult terrain’. Ignoring difficult terrain doesn’t grant a player the ability to move at their normal speed while swimming — only a swim speed does.