Any character can wade in relatively calm water that isn’t over his head, no check required. Similarly, swimming in calm water only requires Swim skill checks with a DC of 10. Trained swimmers can just take 10. Remember, however, that armor or heavy gear makes any attempt at swimming much more difficult (see the Swim skill description).
By contrast, fast-moving water is much more dangerous. Characters must make a successful DC 15 Swim check or a DC 15 Strength check to avoid going under. On a failed check, the character takes 1d3 points of nonlethal damage per round (1d6 points of lethal damage if flowing over rocks and cascades).
Very deep water is not only generally pitch black, posing a navigational hazard, but worse, deals water pressure damage of 1d6 points per minute for every 100 feet the character is below the surface. A successful Fortitude save (DC 15, +1 for each previous check) means the diver takes no damage in that minute. Very cold water deals 1d6 points of nonlethal damage from hypothermia per minute of exposure.
Large, placid rivers move at only a few miles per hour, so they function as still water for most purposes. But some rivers and streams are swifter; anything floating in them moves downstream at a speed of 10 to 40 feet per round. The fastest rapids send swimmers bobbing downstream at 60 to 90 feet per round. Fast rivers are always at least rough water (Swim DC 15), and whitewater rapids are stormy water (Swim DC 20). If a character is in moving water, move her downstream the indicated distance at the end of her turn. A character trying to maintain her position relative to the riverbank can spend some or all of her turn swimming upstream.
Swept Away: Characters swept away by a river moving 60 feet per round or faster must make DC 20 Swim checks every round to avoid going under. If a character gets a check result of 5 or more over the minimum necessary, she arrests her motion by catching a rock, tree limb, or bottom snag-she is no longer being carried along by the flow of the water. Escaping the rapids by reaching the bank requires three DC 20 Swim checks in a row. Characters arrested by a rock, limb, or snag can’t escape under their own power unless they strike out into the water and attempt to swim their way clear. Other characters can rescue them as if they were trapped in quicksand (see Marsh Terrain.)
Any character can hold her breath for a number of rounds equal to twice her Constitution score. If a character takes a standard or full-round action, the remaining duration that the character can hold her breath is reduced by 1 round. After this period of time, the character must make a DC 10 Constitution check every round in order to continue holding her breath. Each round, the DC increases by 1.
When the character finally fails her Constitution check, she begins to drown. In the first round, she falls unconscious (0 hp). In the following round, she drops to -1 hit points and is dying. In the third round, she drowns.
Unconscious characters must begin making Constitution checks immediately upon being submerged (or upon becoming unconscious if the character was conscious when submerged). Once she fails one of these checks, she immediately drops to -1 (or loses 1 additional hit point, if her total is below -1). On the following round, she drowns.
It is possible to drown in substances other than water, such as sand, quicksand, fine dust, and silos full of grain.
See also: Fast-flowing water
In many wilderness areas, river floods are a common occurrence. In spring, an enormous snowmelt can engorge the streams and rivers it feeds. Other catastrophic events such as massive rainstorms or the destruction of a dam can create floods as well.
During a flood, rivers become wider, deeper, and swifter. Assume that a river rises by 1d10+10 feet during the spring flood, and its width increases by a factor of 1d4 × 50%. Fords might disappear for days, bridges might be swept away, and even ferries might not be able to manage the crossing of a flooded river. A river in flood makes Swim checks one category harder (calm water becomes rough, and rough water becomes stormy). Rivers also become 50% swifter.
Additional Flooding Information
Heavy rains can cause rivers to swell and break free of their banks, turning valleys to rushing mudflows and filthy lakes. Experienced guides know to stay clear of rivers during rainstorms, but tropical storms often erupt quickly, and the torrential downpour can catch adventurers in a flash flood without warning. At other times, a storm some distance away can push swelling water down the river and catch travelers in a rushing wall of water.
A traveler can make a DC 20 Survival check to notice the telltale rise in water or other dangerous conditions that signal an impending flash flood. Success means the traveler and her allies have 1d4 rounds to prepare or reach high ground before the flood strikes. A flash flood sweeps past at a speed of 60 feet with enough force to knock down trees and toss boulders around (see Fast-Flowing Water for rules pertaining to potentially being swept away.) At the GM’s discretion, characters caught in a flash flood might suffer additional effects, outlined below.
Characters within 50 feet of a flash flood must make a DC 12 Reflex save or take 2d6 points of damage from hurtling debris. Any character wading through a river or within 10 feet of the river’s edge is caught in the flash flood when it erupts and is subjected to a bull rush (CMB +20). A successful bull rush indicates the character is swept away, taking 2d6 points of damage per round (a DC 12 Reflex save each round negates this damage). Swim checks are possible in a flash flood, but they are difficult due to the churning, raging waters and should be treated as stormy water (see Fast-Flowing Water), with DC 20 Swim checks required to move through the torrent. Most flash floods last 3d6 minutes before subsiding, but on occasion longer flash floods may occur. It’s also important to note that certain animals may sense an impending flood before adventurers, and even if the player characters manage to reach the safety of high ground, they find themselves face to face with other jungle denizens who aren’t interested in sharing it.