Combat underwater presents unique challenges and considerations. These modified rules aim to make underwater combat more engaging and manageable for both players and DMs. We’ve gathered all the related rules into a single spot to make them easier to find, track, and play, ensuring a smooth and immersive experience during underwater encounters.
Breathing Underwater
A character can hold their breath for a number of rounds equal to their Constitution modifier times ten, plus an additional ten rounds. For example, a character with a Constitution modifier of +2 can hold their breath for (2 x 10) + 10 = 30 rounds.
Drowning Check
When a player gets hit underwater while holding their breath, they must make a Constitution saving throw with a DC of 10 or half the damage taken, whichever is higher, similar to a concentration check.
On a successful saving throw, the character maintains their breath. On a failed save, the character rolls a d8 and subtracts the result from the number of rounds they have left to hold their breath.
Drowning
When a character has zero rounds of breath left, they start drowning. At the start of their turn, the character takes two levels of exhaustion each round until they can breathe again, or they die.
Recovery
Recovery from exhaustion follows the standard rules. Each long rest reduces exhaustion by one level.
Combat & Attack Rolls
Melee Attacks. A creature without a swim speed has disadvantage on melee attack rolls unless the weapon is a dagger, javelin, shortsword, spear, or trident.
Ranged Attacks. A creature without a swim speed automatically misses a target beyond the weapon’s normal range. Even within the normal range, the attack roll is made with disadvantage unless the weapon is a crossbow, net, or a weapon that is thrown like a javelin (including a spear, trident, or dart).
Casting Spells
Verbal Components. Casting spells with verbal components underwater may require special considerations. DMs can decide if characters need to be able to breathe underwater to use these spells effectively.
Fire Spells. Spells that deal fire damage may be less effective or not work at all underwater, depending on the DM’s discretion.
Visibility
Light. Underwater environments can range from brightly lit to completely dark. Traditional light sources such as torches may not work well underwater. Characters might need magical light or bioluminescent creatures to see.
Obscurement. Water can cause partial or full cover depending on its clarity and depth.
Movement
Swim Speed. Creatures with a swim speed can move through water without penalty. Those without a swim speed move at half their normal movement rate.
Difficult Terrain. Water is considered difficult terrain for creatures without a swim speed.
By incorporating these rules, we aim to enhance the realism and tension of underwater combat, providing a more immersive and challenging experience for players.
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