Underwater and Swimming Rules Explained: D&D 5e

Featured underwater swimming D&D 5e rules image credit to Wizards of the Coast’s D&D 5e Dungeon Master’s Guide.
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Prepare for underwater combat! Underwater rules of D&D 5e don’t come up often, but I wish I knew them better each time they do. I’ve reviewed them and summarized them in this one spot to help other DMs and players.

In addition to these rules, I highly recommend Opal’s articles about seafaring characters and campaign ideas:

• Multiclassed seafaring character concepts
• How to prep sea adventures + free adventure module

Underwater Visibility (DMG 117)

I’d wager this is one of the most obscure, unreferenced rules in D&D 5e. Despite its rarity, these rules are useful for running underwater encounters.

My D&D group recently brought up these rules as they were relevant to our session when I swam in a lake at night and fought a seafaring creature. The lack of visibility was spectacularly spooky.

This reference table in the DMG is for players who possess light sources, but darkvision will apply. Perception checks roll with disadvantage in dim light, so even darkvision characters need to beware ambushes.

• Clear water, bright light: 60-foot visibility to notice an encounter.
• Clear water, dim light: 30-foot visibility to notice an encounter.
• Murky water or no light: 10-foot visibility to notice an encounter.

I wholeheartedly agree that being underwater will limit visibility. This is the video I think of when I consider underwater visibility.

Underwater Combat (PHB 198)

You roll melee weapon attacks with disadvantage underwater except in the following cases:

• The character has a swimming speed.
  • Riding a mount that possesses a swimming speed does not cancel the disadvantage of your underwater melee weapon attacks.
• The weapon is a dagger, javelin, shortsword, spear, or trident.

Ranged weapon attacks automatically miss if the target is beyond the weapon’s normal range. For example, a longbow would automatically miss beyond 150 feet since its range is 150/600. You roll ranged weapon attacks with disadvantage underwater unless the weapon is a crossbow, net, dart, javelin, spear, trident, or other thrown weapon.

Any creature fully immersed in water will resist fire damage.

Underwater spell attacks roll as normal without disadvantage. Only weapon attacks get disadvantage.

If you want to cast a spell underwater that requires verbal components, you can do that. Doing so means you’ll stop holding your breath and start suffocating. In D&D 5e, suffocating means you die in a number of rounds equal to your Constitution modifier. It’s extremely risky to cast a spell in this way and begin suffocating (source: Jeremy Crawford tweet). Casting Water Breathing will allow you to freely cast spells with verbal components underwater without suffocating.

You can find rules about suffocating on p.183 of the PHB. Holding your breath can last 1+Con modifier in minutes (not rounds). When you can’t hold your breath anymore, you begin to suffocate. Suffocating means you drop to zero hitpoints and begin dying if you don’t reach air in a number of rounds (not minutes) equal to your Con modifier (minimum one round). This happens at the start of your next turn after you run out of rounds.

Long-Distance and Prolonged Swimming (DMG 116)

It’s possible to become exhausted during prolonged swimming. You roll a Constitution saving throw (DC 10) for each hour spent swimming. Failing this saving throw will result in one level of exhaustion for the character. The rules place a hard limit on swimming for eight hours, specifically stating a character cannot swim for that long.

Characters with swimming speeds can swim all day without penalty. They use the forced march rules from the PHB in this case.

Diving through Deep Water (DMG 116)

Similar to the dangers of adventuring in high altitudes, adventurers must beware of intense pressure and freezing temperatures while diving. Creatures that lack swimming speeds will treat each hour of swimming at least 100 feet below the surface as if it were two hours of land travel for the sake of determining exhaustion. In other words, creatures without swimming speeds need to work twice as hard to dive deep.

This ratio intensifies below 200 feet, where each hour of swimming will count as four hours of land travel for the sake of determining exhaustion. That’s clearly an intense aquatic experience, and it assumes a character can breathe or hold its breath for that long (if it needs to at all). Having a swim speed will mean a character’s exhaustion is determined by the normal rules for travel and exhaustion.

Falling into Water (TCoE 170)

Tasha’s suggests that a creature falling into water (or any liquid) can use its reaction to make an Athletics or Acrobatics skill check at DC 15. Succeeding at this saving throw will halve the fall damage taken as the character successfully dives head or feet first into the water (avoiding a deadly bellyflop).

Questions?

Did I answer your questions, or do they yet linger? Cast Message in the comments to tell me about your rules dilemma so I can assist you. I love hearing about fringe questions, so I can consider them for my own games (plus, I like helping you come to your own conclusions).

Have an excellent weekend of adventure, and I’ll see you in the next article.