Aquatic Terrain

Aquatic environments are among the most challenging for PCs short of other worlds and unusual planes. PCs in an aquatic environment need a way to breathe (typically a water breathing spell) and must usually Swim to move, though a PC who sinks to the bottom can walk awkwardly, using the rules for greater difficult terrain.

• Terrain:  typically requires a boat or a swim speed; depends on the strengths of currents and the weather 
• Resources seafood, coral, pearls, shipwrecks 
• Secrets remote islands filled with monsters, isolated communities, pirates, flooded or underwater cities of aquatic creatures

Manifestation

Currents and Flowing Water

Ocean currents, flowing rivers, and similar moving water are difficult terrain or greater difficult terrain (depending on the speed of the water) for a creature Swimming against the current. At the end of a creature’s turn, it moves a certain distance depending on the current’s speed. For instance, a 10-foot current moves a creature 10 feet in the current’s direction at the end of that creature’s turn.

Visibility

It’s much harder to see things at a distance underwater than it is on land, and it’s particularly difficult if the water is murky or full of particles. In pure water, the maximum visual range is roughly 240 feet to see a small object, and in murky water, visibility can be reduced to only 10 feet or even less.

Aquatic Combat

• You’re flat-footed unless you have a swim speed.
• You gain resistance 5 to acid and fire.
• You take a –2 circumstance penalty to melee slashing or bludgeoning attacks that pass through water.
• Ranged attacks that deal bludgeoning or slashing damage automatically miss if the attacker or target is underwater and piercing ranged attacks made by an underwater creature or against an underwater target have their range increments halved.
• You can’t cast fire spells or use actions with the fire trait underwater.• Some ground-based actions might not work underwater or while floating.

Drowning and Suffocating

You can hold your breath for a number of rounds equal to 5 + your Constitution modifier. Reduce your remaining air by 1 round at the end of each of your turns, or by 2 if you attacked or cast any spells that turn. You also lose 1 round worth of air each time you are critically hit or critically fail a save against a damaging effect. If you speak (including casting spells with verbal components or activating items with command components) you lose all remaining air.
When you run out of air, you fall unconscious and start suffocating. You can’t recover from being unconscious and must attempt a DC 20 Fortitude save at the end of each of your turns. On a failure, you take 1d10 damage, and on a critical failure, you die. On each check after the first, the DC increases by 5 and the damage by 1d10; these increases are cumulative. Once your access to air is restored, you stop suffocating and are no longer unconscious (unless you’re at 0 Hit Points).

Type

Natural