Dungeon Master Assistance

Swimming & Combat Above, In, and Under Water

I have previously posted my D&D 5E House Rules rules on for drowning, casting spells underwater, and entire supplements on running nautical adventures. I have recently given more thought to these matters. I have never adequately presented rules to handle issues such as standing above the water and attacking a creature below the water. In this post I address this and other issues as well as reimagining some of my earlier rules. Enjoy!

A few words about “Swim Speed”
• Having a swim speed does more than effect your speed when you are swimming. It implies a familiarity with the underwater environment that effects other things you do underwater such as speaking and using weapons. These abilities are reflected in the sections below.

How fast do you swim?
• Unless you have a swim speed, your movement speed is halved.

Swimming in Armor
• Light Armor: Requires a DC 10 Strength (Athletics) check each round. Failure means you have a speed of 0 for that round.
• Medium Armor: Requires a DC 15 Strength (Athletics) check each round. Failure means you have a speed of 0 for that round and you sink 10 feet.
• Heavy Armor: Requires a DC 20 Strength (Athletics) check each round. Failure means you have a speed of 0 for that round and you sink 20 feet.

Swimming to Exhaustion
• You must make a DC 10 Constitution saving throw each hour that you are swimming or you gain one level of exhaustion. The check is made every half hour if wearing medium armor or every 15 minutes if wearing heavy armor.

Holding Your Breath
• You can hold your breath for a number of minutes equal to 1 + your Constitution modifier. If you have a Constitution score of less than 10 you can hold your breath for 30 seconds. At that point, you fall unconscious.
• When you don’t have time to prepare to enter the water, like if you were surprised, the time that you can hold your breath is halved, to a minimum of 30 seconds.
• Once unconscious, you can survive for a number of rounds equal to your Constitution modifier (minimum of 1 round.) At that point, you drop to zero hit points, begin to drown and must start making death saving throws.
• When drowning, a you cannot regain hit points or be stabilized until you are once again able to breathe.
• When in combat, if you take any action other than the dodge action, at the end of combat you lose 1 minute from the time that you can hold your breath. For a long combat, for every 10 rounds you lose 2 additional minutes.
• When you are hit, you must make a DC 12 Constitution saving throw. On a failure you lose an additional 30 seconds from the time you can continue to hold your breath. If it was a critical hit, you must instead make a DC 20 Constitution saving throw. On a failure you loose your breath and fall unconscious.

Melee Weapons
• When your target is underwater, if you don’t have a swim speed, your weapon attacks are made at disadvantage unless you attack with a dagger, javelin, shortsword, spear, or trident. And your unarmed strikes are made at disadvantage.

Ranged Weapons
• If your target is underwater, all ranged weapon attacks other than crossbows, nets, javelins, spears, tridents, and darts are made with disadvantage and even for these, attacks made beyond the weapon’s normal range automatically miss.

Shooting and Casting Spells Into Water
• From the point of view of a creature out of the water, creatures that are underwater are considered to have 3/4 cover (+5 to the creature’s AC).

Speaking or Casting Spells While Underwater
• Speaking underwater expends some of your air. Each round that you speak or attempt to cast a spell with a verbal component removes 30 seconds from the time you can hold your breath. If you are talking, this can be no more than about 10 words.
• You are harder to understand when you talk while underwater. If you don’t have a swim speed, there is a 50% chance that you won’t be understood when speaking, and a 50% chance that your spell will fail when uttering the verbal component.
• Sound travels further underwater. The verbal component of a spell will be heard at least 40 feet away. The same for normal speech. Anyone further than 40 feet away will have to succeed in a perception check with a DC = the number of feet beyond 40 feet to understand what is said.
• You can’t whisper or yell underwater.
• Creatures that aren’t in the water with you can’t hear you well. If you don’t have a swim speed and you are underwater, anyone that is not in the water will not be able to understand anything that you are saying.
• If you can breathe underwater you can talk and cast spells without restriction.

Fire Spells
• All creatures have resistance to fire damage when submerged underwater.
• The range and AoE of fire spells are both halved. In the case of AoE spells, creatures have advantage on their saving throw.

Lightning Spells
• Creatures have disadvantage when attempting to make a save against an AoE lightning spell. The range and AoE of lightning spells are doubled underwater.

Spells and Magic Items:

Water Walk [PHB p. 287]
3rd-level transmutation (ritual)
Casting Time: 1 Action Ritual
Range: 30 ft
Components: V, S, M (a piece of cork)
Duration: 1 Hour
This spell grants the ability to move across any liquid surface – such as water, acid, mud, snow, quicksand, or lava – as if it were harmless solid ground (creatures crossing molten lava can still take damage from the heat). Up to ten willing creatures you can see within range gain this ability for the duration.
If you target a creature submerged in a liquid, the spell carries the target to the surface of the liquid at a rate of 60 feet per round.

Ring of Water Walking [DMG p. 193]
Ring, uncommon
While wearing this ring, you can stand on and move across any liquid surface as if it were solid ground.

House Rules for the Water Walk spell.
The second part applies only when you target a creature submerged in a liquid, i.e. at the time of casting.

House Rules for Ring of Water Walking
• This does not mention the “Water Walk” spell. The spell says “as if it were harmless solid ground”. Note that the word “harmless” has been omitted from the ring’s description. So walking across acid or any other harmful liquid would inflict damage. It also won’t carry you to the surface if you put it on while underwater.

House Rules for both the Water Walk spell and the Ring of Water Walking
• You can chose to dive under the water whenever you choose. In combat, this will be considered part of your move action.
• If you are underwater and swim to the surface, it will take an action to climb back onto the surface of the water.
• The effect of the spell or the ring will allow you to stand, walk, run, jump or engage in combat. It will also support the weight of your body and everything you are carrying even if you aren’t on your feet. So you can sit, lay down, or stand on your hands or head if that is what you want to do. Any object you are carrying can enter the water as it normally would if your intention is not to support your weight with it. As an example, you could use a walking stick or crutch and a monk could do a kick jump with his staff.
• Your movement is not affected by the current. But, the surface of the water can change (such as with the tide) so the surface you are walking can raise or lower with the surface of the water. This means that waves will cause the surface to rise and fall. Breaking waves could present a problem.
• While you are on the surface you can attack any underwater creature that is within range with your sword or ranged weapon.
• While you are on the surface you can dip up some water in a bowl or even with your hands. You can also reach under the surface to do other things with your hands such as picking up items that you can reach, or open a chest.
• Don’t forget and set your backpack down beside you, it will sink!