Underwater Combat

Underwater Combat

When making a melee weapon attack, a creature that doesn’t have a swimming speed (either natural or granted by magic) has disadvantage on the attack roll unless the weapon is a dagger, javelin, shortsword, spear, or trident.

ranged weapon attack automatically misses a target beyond the weapon’s normal range. Even against a target within normal range, the attack roll has disadvantage unless the weapon is a crossbow, a net, or a weapon that is thrown like a javelin (including a spear, trident, or dart).

Creatures and objects that are fully immersed in water have resistance to fire damage.

Swimming

While climbing or swimming, each foot of movement costs 1 extra foot (2 extra feet in difficult terrain), unless a creature has a climbing or swimming speed.  Additional water terrain features, such as currents, waves, a whirlpool, etc. could make swimming more difficult and may effect speed, and may require swim (athletics checks) – DM Discretion. 

 

Holding your Breath

You can hold your breath for a number of minutes equal to 1 + your Con modifier, as soon as that timer runs out (or if you’re choking/being choked) you have a number of rounds equal to 1 + your Con modifier (minimum of one round), and once that runs out you are Suffocating, which is not where you want to be. According to the PHB, this means you immediately drop to 0 hit points (regardless of your previous total or any resistances/immunities) and you’re dying. You can’t regain hp or be stabilized until you can breathe. It’s rough folks.

Source: https://www.belloflostsouls.net/2019/01/dd-underwater-combat.html

 

Casting Spells Underwater

Spells with Somatic and Material components, sure, no problem, but most spells have a verbal component. Short answer: yes. Long answer: yes, but if you’re talking a lot you’re not holding your breath and that’s something to be careful about, depending on the DM at your table. At this table, if you are casting without the ability to breathe underwater, you will need to succeed on a Concentration check to succeed on the spell and  failing by 5 or more will mean that you start suffocating. Concentratration check is DC 10 plus the level of the spell being cast. 

Updated 11/18/19, Definitive JC Tweet – RAI:

You can cast a single spell underwater, but afterwards you begin drowning if you can’t breathe underwater. Otherwise, no rule prevents verbal components from working underwater.

And in this case, it is Con mod rounds only, (without the +1). The +1 only happens when you’ve held your breath and have Con mod + 1 minutes before you start drowning. So if you had a zero or less on Con mod, and cast a spell, you suffocate at the start of your next turn. 

 

Suffocating

A creature can hold its breath for a number of minutes equal to 1 + its Constitution modifier (minimum of 30 seconds).

When a creature runs out of breath or is choking, it can survive for a number of rounds equal to its Constitution modifier (minimum of 1 round). At the start of its next turn, it drops to 0 Hit Points and is dying, and it can’t regain Hit Points or be stabilized until it can breathe again.

For example, a creature with a Constitution of 14 can hold its breath for 3 minutes. If it starts suffocating, it has 2 rounds to reach air before it drops to 0 Hit Points.