Movement - Underwater (OSS)

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Surface dwellers suffer a distinct disadvantage when attempting to move underwater. Currents, pressure, and resistance severely limit a creature's ability to travel in a watery environment. Of course, magical items (such as a ring of free action) and magic spells (like teleport) can partially or completely negate such difficulties. However, characters without magical assistance must either find a solid surface upon which to walk, or swim to their destinations.
==Swimming Underwater==
Adventurers who decide to swim underwater face a difficult task. Water resistance and the additional weight of adventuring gear combine to slow the progress of a swimming character. Nonproficient swimmers (adventurers who do not possess the Swimming proficiency) flail their arms and legs wildly and swim at a rate equal to one third of their current land movement times five in yards. Thus, a nonproficient dwarf could swim at a rate of 10 yards (6+3=2x5=10) or 30 feet in one round.
If the optional encumbrance rules (see PHB, Chapter 6) are in force, nonproficient characters must qualify as unencumbered to move even at this slow a pace. Encumbered nonproficient swimmers (even lightly encumbered ones) cannot swim any distance they are stuck at the bottom of the river, lake, or sea.
Characters with the Swimming proficiency can swim at a rate equal to one half of their land movement times five in yards. Thus, a proficient dwarf could swim up to 15 yards (6+2=3x5=15) or 45 feet in a single round.
Note that proficient swimmers can still swim while encumbered if the optional encumbrance category rules are in force. Lightly encumbered proficient swimmers travel at one third of their land movement rates times five in yards. Moderately (and more heavily) encumbered characters cannot swim until they jettison the extra weight.
Under no circumstances should a Dungeon Master allow a character in nonmagical metal armor to swim. Simply put, the weight of such armor and its restriction of limb actions make it impossible for even the most proficient swimmer to move while wearing it.
===Surfacing===
During the course of an adventure, it may become necessary for a submerged character to rise to the surface. As a simple rule, all actively swimming characters can ascend at their maximum underwater swimming rates. Characters simply floating to the surface unconscious characters, for example-rise at a rate of 10 feet per round. However, if the DM uses the optional encumbrance rules, encumbered characters cannot simply float to the surface. If these characters do not actively swim, they sink (see below).
===Sinking===
Sinking characters descend at a rate of 10 feet per round. This rate of descent increases to 40 feet per round if a character wears metal armor or carries more than 30 pounds of equipment. Characters swimming straight down descend at their current swimming rates and can add their sinking rates to their downward movement each round.
===Maximum Depth===
Because pressure increases dramatically as depth increases, player characters and many other creatures cannot function very far below the surface without magical assistance or specific biological adaptations. Table 43: Maximum Functioning Depth shows the maximum depth at which unassisted player character races can still function (fight, cast spells, explore, etc.) in relation to other more adapted creatures and monsters.
Through force of will, luck, and sheer physical endurance, PCs (and other creatures) without magical assistance can extend their maximum functioning depths. The danger such action poses, however, is quite grave; the pressure of the ocean depths can easily crush surface dwellers who travel too far out of their element.
Once any creature moves beyond its maximum depth, it must make a successful saving throw vs. paralyzation to resist the detrimental effects of pressure. The creature must attempt the saving throw at the end of each turn it remains below its maximum depth. Failure indicates that the creature suffers 4d10 points of crushing damage per round, plus 1d10 points of damage for each Depth Unit below the creature's maximum depth.
A Depth Unit is a number of feet equal to the particular creature's maximum depth. (Thus the exact value of each creature's Depth Unit varies with the creature.) For example, the Depth Unit for a dwarf is 600 feet. If a dwarf fails his saving throw vs. paralyzation, he suffers 4d10 plus an additional 1d10 points of damage at depths of 601 to 1199 feet. At depths between 1200 and 1799 feet, a failed save would cause a dwarf 4d10 plus an additional 2d10 points of damage, as he would be 2 Depth Units beyond his maximum.
A successful saving throw vs. paralyzation, however, indicates that the PC in question can function at an additional Depth Unit-albeit less efficiently-for up to one day. The creature can withstand the pressure at the new depth even if it subsequently descends another Depth Unit and fails its save.
Even with successful saving throws, creatures functioning beyond their maximum depths do so with a -1 penalty to initiative rolls, attack rolls, saving throws, and ability checks for each Depth Unit beyond the first.
These penalties are in addition to the standard underwater penalties described earlier in this chapter.
===Maximum Functioning Depth by Race===
Note that the greatest dichotomy in the depth limits for demihumans occurs between elves and dwarves. Elves, with their lighter physiology, cannot withstand the rigors of pressure as well as other races. Dwarves, on the other hand, possess thick bones and a stronger musculature; these characteristics allow them (ironically, considering their attitudes about water) to resist the effects of pressure and function with the most ease.
For example, Marlon, a human rogue, finds herself adventuring 300 feet below the surface of the water. According to Table 43: Maximum Functioning Depth, Marlon can function quite normally while at this depth. (Her normal maximum depth is 400 feet.) However, the young rogue spots something shiny in the water 120 feet below her and swims down.
After Mailon spends one turn at the increased depth, her player rolls the die and gets a 17. Success! Marlon has resisted the negative effects of pressure and can now function at an additional Depth Unit (with a -1 penalty to most die rolls for being 1 Depth Unit beyond her maximum depth). According to Table 43, Marlon's Depth Units occur at 400 feet intervals. Because of her successful saving throw, she can resist the crushing effects of pressure for an additional 400 feet (from 401 to 800 feet) for one day. If she passes beyond 800 feet (and stays at that depth for more than a turn), the rogue must make another saving throw vs. paralyzation (with a -1 penalty). If she fails, Marlon suffers 6d10 points of damage per round (4d10 for failing her save plus 2d10 for being two Depth Units beyond her normal maximum). Marlon would stop taking crushing damage once she reached 800 feet or above, as she had previously acclimated to that depth by making her saving throw vs. paralyzation.
Of course, certain magical items and magic spells can extend a character's maximum functional depth-sometimes indefinitely. For details, see Chapters 7 and 8.
===Swimming and Maneuverability===
An excursion underwater is a journey through a completely alien environment and even the most accomplished swimmers must be prepared to deal with a few limitations. Most character races are not built for speed or maneuverability underwater. Therefore, certain actions become more difficult to perform while swimming underwater.
A character must attempt a Dexterity check when performing abrupt or complex maneuvers underwater. Failure indicates that the character cannot perform the action until the end of the next round. Such actions might include turning to face an enemy, grabbing for a spare weapon, or coming to a sudden full stop after moving at top speed. Nonproficient swimmers suffer a -4 penalty to the roll.
For example, a marine troll attacks Corinna from behind as she swims away from the temporary shelter of some underwater caves. Corinna's player makes a Dexterity check (the character has a Dexterity of 16) and rolls a 17. She fails; therefore Corinna is unable to turn around and face her attacker until the end of the next round, giving the marine troll first strike in the next round.
===Swimming and Endurance===
Swimming underwater is just as tiring as surface swimming. As with the latter, the length of time that a character can swim while underwater depends on his Constitution score. See the section on Swimming in Chapter 14 of the Player's Handbook for details.
There is, however, one notable change to the swimming rules: Characters regain Strength and Constitution points lost due to prolonged swimming or speed increases at one-half the normal rate while submerged. For each full day of rest, a character regains 1d3 Constitution points. If a character has lost both Constitution and Strength points from swimming, the character regains only 1 point in each ability for every day of rest.
For example, Corinna, a paladin, has an effective Constitution score of 10 after several tiring hours spent swimming toward a series of undersea caves. Once in the caves, she decides to rest for a day. Her player rolls 1d3 and gets a 2. After her day of rest, Corinna regains 2 points of Constitution.
In addition to regaining lost ability score points, a character may also reduce attack penalties incurred through extensive swimming. For each full day of rest, a character may remove 1d3 points of attack penalties.
In all cases, "rest" assumes adequate food and water, as well as a semi-comfortable place to recuperate. For example, a soft, flowing bed of kelp would allow a character to rest adequately. A tiny cave full of sharp stalagmites and other dangerous debris, on the other hand, would prove insufficient for a character needing to recuperate.
==Walking==
Walking is another common method of underwater locomotion that surface dwellers use. The ability to walk underwater presupposes a solid surface-such as a lake bottom or underwater ridge and some method of remaining firmly attached to that surface. The weight of adventuring equipment or other ballast (rocks, treasure, etc.) usually suffices.
A character can walk at a rate equal to one third of his land movement times five in yards per round. A human walking underwater could travel 20 yards (12+3=4x5=20) or 60 feet a round, a rate of underwater travel equivalent to that of a nonproficient swimmer. However, walking characters do not lose Constitution points as do swimmers. In addition, PCs who walk can turn to face attackers without making Dexterity checks.