UNDERWATER RULES

Holding Your Breath

• A character who takes a deep breath can hold their breath for 60 seconds per point of con modifier (minimum 30 seconds) if they are engaging in minimal activity

• Each time the character takes damage, their air capacity is reduced by 30 seconds.

• Speaking or casting a spell immediately empties the air from the character's lungs

• A character who is under the effects of the Water Breathing spell does not have any air stored in their lungs, but their lungs are also not filled with water.  

  • If the spell ends suddenly while underwater, they will start the first round of suffocation at the start of their next turn.
    
    

Suffocating

• A character who is out of air suffers 1d6 points suffocation damage on the first round.  

  • This damage is repeated each round and increased by 1d6 for each subsequent round they are out of air.

Swimming in water costs twice as much movement unless you have a swim speed. 

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.

A 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. 

Endurance

• For each hour swimming, you need to make a constitution saving throw or suffer a point of exhaustion

  • Near Surface (DC 10)

  • 100 feet below surface (DC 15)

  • 200 feet below surface  (DC 20)

Visibility

• Clear Water + Bright Light - 60 feet

• Clear Water + Dim Light - 30 feet

• Murky Water or No Light - 10 feet

  • Reminder that perception checks are at disadvantage in dim light.  Darkvision improves light by one category.