Aquatic terrain is the least hospitable to most PCs, because they can’t breathe there. Aquatic terrain doesn’t offer the variety that land terrain does. The ocean floor holds many marvels, including undersea analogues of any of the terrain elements described earlier in this section.
Nonflowing Water: Lakes and oceans simply require a swim speed or successful Swim checks to move through (DC 10 in calm water, DC 15 in rough water, DC 20 in stormy water). Characters need a way to breathe if they’re underwater; failing that, they risk drowning. When underwater, characters can move in any direction as if they were flying with perfect maneuverability.
Stealth and Detection Underwater: How far you can see underwater depends on the water’s clarity. As a guideline, creatures can see 4d8×10 feet if the water is clear, and 1d8×10 feet if it’s murky. Moving water is always murky, unless it’s in a particularly large, slow-moving river.
It’s hard to find cover or concealment to hide underwater (except along the seafloor). Listen and Move Silently checks function normally underwater.
Invisibility: An invisible creature displaces water and leaves a visible, body-shaped “bubble” where the water was displaced. The creature still has concealment (20% miss chance), but not total concealment (50% miss chance).
Water Pressure: In the LSJ campaign, magic that allows water breathing also is assumed to confer limited protection against the hazards of water pressure. Multiply the caster level of the spell, ability, or item times fifty feet to determine the depth to which the subject is protected. For example, a helm of underwater action (CL 5th) allows the wearer to operate safely at depths up to 250 feet; a water breathing spell cast by an 11th level cleric would confer protection to its subject up to depths up to 550 feet. Beyond these depths, use the difference to calculate the level of hazard per the d20 SRD environmental danger rules.
Land-based creatures can have considerable difficulty when fighting in water. Water affects a creature’s Armor Class, attack rolls, damage, and movement. In some cases a creature’s opponents may get a bonus on attacks. The effects are summarized in the accompanying table. They apply whenever a character is swimming, walking in chest deep water, or walking along the bottom.
Ranged Attacks Underwater: Thrown weapons are ineffective underwater, even when launched from land. Attacks with other ranged weapons take a –2 penalty on attack rolls for every 5 feet of water they pass through, in addition to the normal penalties for range.
Attacks from Land: Characters swimming, floating, or treading water on the surface, or wading in water at least chest deep, have improved cover (+8 bonus to AC, +4 bonus on Reflex saves) from opponents on land. Land bound opponents who have freedom of movement effects ignore this cover when making melee attacks against targets in the water. A completely submerged creature has total cover against opponents on land unless those opponents have freedom of movement effects. Magical effects are unaffected except for those that require attack rolls (which are treated like any other effects) and fire effects.
Fire: Nonmagical fire (including alchemist’s fire) does not burn underwater. Spells or spell-like effects with the fire descriptor are ineffective underwater unless the caster makes a Spellcraft check (DC 20 + spell level). If the check succeeds, the spell creates a bubble of steam instead of its usual fiery effect, but otherwise the spell works as described. A supernatural fire effect is ineffective underwater unless its description states otherwise. The surface of a body of water blocks line of effect for any fire spell. If the caster has made a Spellcraft check to make the fire spell usable underwater, the surface still blocks the spell’s line of effect
| ————— Attack/Damage ————— | ||||
|---|---|---|---|---|
| Condition | Slashing or Bludgeoning | Tail | Movement | Off Balance? (4) |
| Freedom of Movement | Normal / Normal | Normal / Normal | Normal | No |
| Has a swim speed | -2 / Half | Normal | Normal | No |
| Successful swim check | -2 / Half (1) | -2 / Half | Quarter or Half (2) | No |
| Firm footing (3) | -2 / Half | -2 / Half | Half | No |
| None of the above | -2 / Half | -2 / Half | Normal | Yes |
1 A creature without a freedom of movement effects or a swim speed makes grapple checks underwater at a –2 penalty, but deals damage normally when grappling.
2 A successful Swim check lets a creature move one-quarter its speed as a move action or one-half its speed as a full-round action.
3 Creatures have firm footing when walking along the bottom, braced against a ship’s hull, or the like. A creature can only walk along the bottom if it wears or carries enough gear to weigh itself down—at least 16 pounds for Medium creatures, twice that for each size category larger than Medium, and half that for each size category smaller than Medium.
4 Creatures flailing about in the water (usually because they failed their Swim checks) have a hard time fighting effectively. An off-balance creature loses its Dexterity bonus to Armor Class, and opponents gain a +2 bonus on attacks against it.