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Swimming: And all matters concerning being in or below water as per Mystara BECMI D&D

by Robin

According the Rules Cyclopedia all characters may swim, unless the DM decides otherwise.

A character's movement rate is 1/5 his outdoor running speed.

120 yard per round/5=24 yards per round.

A character swimming underwater measures his movement rate in feet. Thus a character who can swim 24 yards per round on the surface can swim at 24' underwater.

Yet many more factors and other rules were introduced in PC3-Creature Crucible-Sea People, rules cyclopedia, and other D&D materials, both canon and fanon, and even my own as seen in Threshold issue 24 page; 91 on the Swimming contest known as the Kylo Run in Karameikos.

Matters like encumbrance, strength, skills, devices, magic, other races, depth, pressure were introduced, along with systems awarity of current and wind yet not combined.

To make clarity in this murky mess of variable rules grouped here and there, the following compilatation of these rules are now merged into one easy system....I hope. 

As can be seen in my other compilation work on skills

Swimming Skill

A character with swimming Skill knows how to swim and can move according to the rules given in the Swimming section. Those without this Skill can’t swim. They can hold their breath and float, but they can’t really move themselves about in the water. Their movement rate is severely hampered.

Most character growing up on or close by water should have a Swimming skill. 

Most characters growing up elsewhere rarely have a swimming skill.(and this was--and often still is--the same in the real world, even in the middleages. In the real world renaissaince period less people could swim than in the Middle-ages and before due religious or political doctrines, something similar could apply to Glantri, and Darokin)

Remember a Swimming skill is a Dexterity based skill. And like any skills are taught (self or other) and learned by trial and error. The limit a character has in this skill is thus his Dexterity as an adult.

This limit may according the skill rules be increased by 1 for each later learned additional skill slot taken by swimming. This is noted as; Swimming +1, Swimming +2, etc.).

For most characters their Swimming Skill will be as high as their last teacher's skill or their own Dexterity at best. 

According the skill rules; The score of any single skill a character has begins with roll 8+1d10, that was the score equal to that taught from the last teacher (which uses its own skillscore as a maximum possible to teach), if this is higher than the ability the character has, the score is derived from the used ability instead. This means a person with a Dexterity of 13 and a taught (rolled ) swimming skill of 16, will have its swimming skill at 13, yet can go beyond this by using an additional skillslot for each point (in this case 3 skillslots from this teacher). Most characters will keep to the basic skillslot however, and use the other slots for other skills.

A Swimming skill seriously affect the swimming speed and duration.

Strength affects swimming speed:  +1 yard/strength adjustment. This means a weak character swims slower while a strong character swims faster

Constitution affects swimming duration (and holding breath)

How Constitution affects swimming duration: 

A PC’s basic swimming duration before exhaustion sets in is 1 hour per constitution point. 

When this time is passed, constitution checks must be made each Turn (1 Turn = 10 minutes = 60 rounds) and Constitution is reduced by 1 for each failed check. When a character’s constitution = 3, nearby boats seeing the struggling character will usually pick them out of the water. If no boat or any other flotation device, magic or swimming animal is available, a character will drown when constitution eventually hits 0 due to hypothermia and exhaustion. 

Keep in mind that holding a flotation device is dependend on the exhaustion level of the character and the severity of waves.

Do not use the normal rules for exhaustion in addition to this system. Instead, a character is fatiqued after the first 3 consecutive failed swimming checks, seriously fatiqued after 6 consecutive failed swimming hecks and exhausted after 9 consecutive failed swimming checks.

When affected by fatique or exhaustion the character can only recuperate if on shore, a boot, or magically adapted to water. Any other way does not rest the character enough to recuperate the fatique, seriously fatique or exhaustion penalties. Keep the normal Fatique and Exhaustion effects and recuperastion periods.


Wind & Current Effects 

Swimming in rough and moving water is more difficult. Swimming along a current and or winddirection adds the windstrength (0 to 9)  and/or the current (1 to 6) to the movement rate. This number is substracted if swimming agains  the wind and or current. A DM must check this before hand. Side winds or currents are not counted, yet do influence the coarse of a character, as they drag the character in that direction. 

Add these contributing factors together as follows; Wind+ Current = same general direction = add together. Wind + Current= Opposite direction= substract lowest from highest and use that.

Wind + Current= sideways= use the one in (add) or against the PC direction (substract), the other one pushes the PC in its own direction sideways; as described here;

Each swimmer character in these conditions must do a swimming check every 500 yards, and a strength check every 100-yard. If either check fails, a constitution check must be made or the swimmer falls back 100 + (10 yards per failed point) yards. 

If the swimming check fails with 8 or more, the swimmer suffers a 500 + (20 yards per failed point) yards setback, and temporarily (lasting 1 day) has their constitution reduced by 1, and an extra swimming skill check to prevent drowning is required. 

Ignore Strength Checks if the wind strength is less than 2, Ignore the above mentioned duration Swimming checks if there is also no current, and make only a skill check initially, and each when the duration becomes longerthan the character's current constitution.

General Wind Strength; 

This rate is based on the Weather table in Rules Cyclopedia page 90, and the Real World windstrenth table
0= No wind, 1= light air, 2=light breeze, 3=gentle breeze, 4=mooderate breeze, 5=fresh breeze, 6= strong breeze/light Storm, 7=moderate gale, 8= fresh gale, 9=strong gale. Everything higher is unable to swim on the surface or even close to it. Any person caught in winds of strength 10 or higher without adequate magical abilities to survive (aka a survival skill + flotation devices) have only an 8%-1 for each windstrength above 10 chance to survive, and be caught dead, so exhausted the character is nearly dead on a shore far, far away or dragged out of the water by a friendly skipper. 
This survival option is a way for a DM to place a character where he want him and bring the character in a new environment and chances for adventure..

Current strength

0= standing water, 1= low flow water, 2= moderate flow water, 3= strong flow water(most creeks, weak rivers), 4=very strong flow water (most strong rivers, sea currents), 5=rapid flow (waterrapids in rivers, some rare currents in sea, close to whirlpool), 6=thunderflow (springflood, ridal flood, tsunami, dam breach, water fall). 

Becoming wounded might lure available sharks or other predators to take a bite or more Any attack (by shark, NPC or otherwise) requires an extra swimming skill check at -4 to prevent losing 400 yards distance.

DMs may incorporate other difficulties like sharp rocks, Rocky Coast, tangled weeds, unexpected creatures; these also require an extra swimming skill check at -2, to prevent losing 200 yards, or to prevent a succesful touching shore and leaving the water, and might wound the character for 1d4, 1d6 or even 2d6.  

A DM may enforrce extra swimming checks in the case of ripcurrents(current which are short, but different from the main current and may be very harmful next to solid objects like boats, rocks, reefs etc)

In a river a DM might ignore wind, and apply the known current speed instead the more general current strength.However, this will change on each section of a rive; towards the flatlands i will ease down and towards rapids, waterfalls or whirpools it will increase. A storm flood, broken dam, tsunami will of course have its own direction and can create massive impact damages, not alone flushing characters away, and tossing them about. Swimming might help a bit, yet is absolutely no guarantee to survive these.


One of the most important factors in swimming is encumbrance. what a character carries. This influences the character's swimming speed, and swimming duration.

Keep in mind that worn clothing (normally not counted in encumbrance) must be counted in water and on the surface until fully dried. Use What can be Bought to find out encumbrance of shoes, clothing, and similar.

The more weight a character carries, the more that same weight will drag that character down.  In the table below this dragging down can be seen in the final column of Swimming Rate and Duration. The character must be able to swim against this drag to remain on the surface of the water. So not only limit this the forward speed of the character, this also drags him down. 

So for example; a character with a Strength of 16(+2), a Constitution of 14(+1), and a Swimming Skill of 15, would be able to swim at (15+24+2)=41 yards per round on the surface, and could maintain that for a maximum of 14 x 6=84 Turns+15 Turns=99 Turns=16.5 hours (not counting other handicaps). The duration underwater is controlled by holding breath. If this is magically enabled to be longer it is the duration of that magic or as above minus the drag.

If the same character would be Light encumbered (in his case between 601 and 1000 cn, due the extra 200cn by his strength) he would be able to swim at (15+18+2)=35 yards per round(105 feet) yet the weight would further drag him down a 10 feet. so his total maximum swimming rate would be 105-10=95 feet =31,66 yards per round on the surface and only 35-10=25 feet per round underwater.
And could maintain that for a maximum of 14 x 6=84 Turns+15 Turns-10 Drag=89 Turns=14.8 hours (not counting other handicaps).

If the same character would be Moderate encumbered (between 1000 and 1400cn, due the extra 200cn by his strength) he would be able to swim at (15+12+2)=29 yards per round(87 feet) yet the weight would further drag him down a 20 feet. so his total maximum swimming rate would be 87-20=67 feet =22.33 yards per round on the surface and only 35-20=15 feet per round underwater.

And could maintain that for a maximum of 14 x 6=84 Turns+15 Turns-20 Drag=79 Turns=13.2 hours (not counting other handicaps).

If the same character would be Heavy encumbered (between 1401 and 2200cn, due the extra 200cn by his strength) he would be able to swim at (15+6+2)=23 yards per round(69 feet) yet the weight would further drag him down a 30 feet. So his total maximum swimming rate would be 69-30=39 feet =13 yards per round on the surface and only 23-30= -7 feet per round underwater(in other words he would sink 7 feet for each round).

And could maintain that for a maximum of 14 x 6=84 Turns+15 Turns-30 Drag=69 Turns=11.5 hours (not counting other handicaps).


Expelling encumbrance takes at least 1 round for most things expelled individually. An armor or heavy garb is expelled after 1 round for each AC improvement (or Armor Value) the armor or garb gives. 

Expelling items is not swimming, and will cause the character to sink the whole unadjusted drag  each round as per total encumbrance at that round. First when the item is fully expelled, the downward drag by encumbrance can be adjusted by the current encumbrance of the character.

Flotation Devices

Keep in mind that some items are able to act as floatation devices. These include any items of wood, empty and closed waterskins, barrels or even coffins or trunks and their normal encumbrance is now counted as a negative. 

So if a character has a 100cn heavy 500cn capacity empty barrel nearby, holding such an item lowers his encumbrance by 600cn. If he would blow up a waterskin (holding when full 25 cn liquid) it would reduce his encumbrance 25cn.

Swimming with a flotation device reduces the swimming speed to the underwater rate, and underwater might cause an upward drag depending on its flotation capacity.

An extreme salty sea can have its own ability of (like the real Dead Sea) preventing drowning, by creating a natural buoancy to life forms, yet will cause severe water deprivation in the character. Each passed hour will count as 3 for determining the required intake of clean not-salty water, to prevent water deprivation.

All the following effects last until the magic ends the normal rules apply~!!!

Ring of Waterbreathing

Magic giving Water Breathing; like the spell, Ring/Potion of Water Breathing

This only prevents drowning, and does not affect anything else.

Magic Giving Freedom; like Ring or spell of Free Action
This gives the character the ability to use weapons as on the surface

Magic giving Swimming; like spell, Ring or belt or footwear of Swimming 

Ring of Swimming
This gives the character a basic Swimming skill equal to its dexterity

Magic giving air around a character; Like the spell Airy water, bubble
This enables the affected character to cast magic underwater, and prevents drowning. It also creates an upward drag of 24 fet/round

Magic or items giving extra speed; Like Haste spell, Potion/Ring of Speed, or flippers.
Flippers (wood or animal material) enables the character to double it normal swimming skill if the character has trained sufficiently in these. A Haste Spell or potion or similar doubles the total swimming speed.
Bowl of Commanding Water Elementals

Magic giving Water Adaptation; like Staff of Elemental Water Adaptation, Ring/staff/bowl of Water Elemental Command

This gives the Character a basic Swimming skill equal to its dexterity and the ability to use weapons as on the surface and the ability to prevents drowning, and cast magic underwater

Magic or items giving buoyancy
These prevent the character from sinking, and thus mostly also from drowning. However these must be attached correctly to the character. if the character is unconcious his/her weight might drag him/her back underwater in unstable or moving water. See above on flotation devices. If underwater it will cause an upward drag of 50 feet per  round

Ring of Waterwalking
Magic giving the ability to walk on water; Like spell, potion, ring or footwear of water walking.

This prevents the character to go underwater. however moving on a moving surface is as difficult as swimming, apply Wind and current effects, and dexterity checks each 500 yards or fall behind as described above. Strength checks and swimming checks are not needed under these circumstances. Running is impossible, and only a walking speed in yards is maximum possible. This magical also creates an upward drag of 50feet per round if underwater.

Magic enabling Survival; like the Survival spell.
This merely prevents the character from drowning, hunger or thirst or lack of air, yet does nothing more. Exhaustion by swimming still applies. As doe impact, misorentation, etc.

Normally spellcasting underwater is NOT possible as magic needs the air to become effective. Afriendly DM could allow a PC to use ALL his breath and cast a single spell while expelling all the air at the same time. This requires of course a succesful ability check depending on the type of spell cast.(Clerical= Wisdom, Magical=Intelligence). When failed or still underwater after the spell is activayed Drowning rules apply..

Magic is possible when adapted to water by being an underwater race (then the same rules apply above water for these creatures), when one is adapted to both surface and underwater (Aquatic Elves, Storm Giants, Sharkkin in their land period, Merrow and Sea Giants the first 3(+con) rounds in the air), When one is undr the influence of Airy Water, Water Adaptation, Bubble magic, but NOT under the influence of Water Breathing. This requires at least 4 months training(+1 month per failed intelligence check at -4) to become adapted to living underwater, and will be lost after 4 months(the same applies for water creatures on the surface if not adapted)

Pressure Resistance           

Range:                        Touch
Base Duration;           1 Turn + 1 Turn / level
Casting Time:              4
Effect:                         creature touched
Component;                Holy Symbol+small prayer
Save:                          None
Known by Clerics of Sea(different races), of Water / Time Immortals. level 2 spell. uncommon
This spell increases the recipient’s resistance to the crushing force of water pressure, allowing him or her to function at greater depths underwater. The spell’s recipient can safely dive to twice his normal depth for each spell used. For example, an unassisted human can normally withstand the effects of pressure to a maximum of 400 feet underwater. A human protected with this spell could safely dive to a depth of 800 feet. The recipient will notice when the limit is reached. To swim deeper a second or third spell will add another base limit to the recipient, which also increases the full duration by the base duration. When this spell is somehow dispelled underwater, the recipient will be instantly vulnerable to the crushing of the water and could die in mere moments. Damages are 1d8hp / 50 feet beyond the limit for the race, each Turn. This spell does not enable water breathing. Most aquatic races know this spell, and some may have an ability with similar effect but unlimted duration to themselves. This spell also removes the harmful effects of caisson disease (see below under Pressure of the Deep), yet the patient must be placed in an enclosed environment (like a barrel) of less than 10 cubic feet, and remain there for the full duration of the spell.
Don't be confused; the term Sea animal in the table only confers to non-fish.
Kraken includes all squid.
Fish will be present in all regions, although adapted to the pressure of their general region. They can go up and down roughly 1000 feet per HD without sustaining damage due pressure differences.
Spermwhales hunt in a single breath, swimming straight down at about 4000 feet holding their breath for 90 minutes. Cuvier's beaked whales are the deepest diving air breathing animals of all Real World scientists tracked one on a dive to 9,874 feet (2,992 m). The dive lasted for 2 hours and 17 minutes, making this whale the longest-diving mammal on record as well as the deepest.We could say the Leviathan whale (see MMMC2; page 498) could assume similar depths.
The Behemoth ( a unique shark as per PWA and MMMC2 page 317-318. some sages describe this monster as a Burrower) only goes to a maximum of 30.000 feet, yet its mass of HP could make it endure greater depth,  Megalodon and cookiecuttersharksSharks go to 3000feet.
Submarine vessels normally go not lower than 1000 feet, with magic this could be tripled at best.beyond that the vessel suffers presurre damage in the same rates. after 50% of its hullpoints it will lose control and leak, taking an additional 1d6 points of damage each 50 feet per Turn(10 minutes).
Other creatures are listed in the MMMC2 and have their maximum depth listed.

Combat in and Underwater (also counts in the Plane of Water, unless in airfilled environments!!)

On the surface all weapons are functional  as normal, although a standard -4 to hit is applied to melee and -6 on missile weapons, due to the instability while in the water and waves. Aquatic creatures attacking on the surface have this also, yet now due the lack of water resistance.

When directing the melee attack from the surface underwater or when attacking underwater the standard -4 to hit is also applied, and Cutting, Slashing, and Smashing melee attacks (this includes all natural attacks) are at an additional -10 to hit, and give only 50% normal total damage, due to the pressure caused by the water itself. Missile weapons like bow only have the standard -6 to hit when attacking from the surface due lightbreaking conditions, and underwater ranges are decreased by 33%.
Crossbows only have the standard -4 to hit, have normal range and damages. 
Abilities as fast draw, multiple attacks are impossible to make underwater with missile weapons.

Thrusting, Piercing melee attacks are as normal although the -4 to hit is still applied

A succesful intelligence check each month staying underwater AND using the weapons regularly can reduce the standard -4 hitroll penalty by 1 to a maximum of 4. For each month thereafter acting on the surface this is reduced again by -1 until it is on the normal -4 after 4 months. This is normal adaptation to a different environment.  The same applies to aquatic beings attacking on the surface.

Breath weapons and most spells only go as deep or far as half the normal range, and give 50% less damage, and saving throws against these are increased by +4.

An exception to this is electricity; this is unhindered in range, yet the effects change; the full range of the spell is used and expelled in a linear direction as intended, and at the end of the range the electricity becomes spheroid in effect. Any object or creature blocking this range caused the spell to end there. A Lightning Bolt becomes a Lightning Ball. For a general rule; this sphere is 1' diameter per HD of the spell, and gives normal damage and uses normal saving throws.

Aquatic casters on the surface using breath weapons or spells see these are double in range and half in damage, with a +4 to saving throws. Electricity cast will completely suprise them as these effects are as normal surface spells and ranges and effects are different.A Lightning Ball becomes a normal Lightning Bolt.

DM's take care in using this on all electrical spells, as some of these are touch-based they will affect the caster underwater unless protected.

Visibility underwater (as per PC3-Creature Crucible-Sea People)

Near the surface of the water there is plenty of light, at least suring the day, but the water distorts the light and reduces visibility. Use the following table to determine visibility in water.


When a character goes underwater, and cannot breath there (or aquatic creature on the surface) he must hold its breath or immediately begin drowning. The character can holds its breath for a number of rounds equal to his current constitution, yet each round of excertion (fighting, panicking, expelling armor,, etc) count as 2 rounds. 

Once a character no longer can holds its breath, the character begins to drown (or suffocate if aquatic). A constitution check must be made each round, with a cumulative penalty of -1 after the first round. The character is at this point exhausted.(THAC0 -2, AC+2, Damage -2 (even 0 is possible), MV 1/3)

Once the character fails this check, he has drowned--but he is not dead yet. Although he does not breath, he will not be dead for a number of rounds equal to 1/3rd his current constitution (round up!!). While in this sate between life and death, the character can be healed in its original environment (on surface if airbreather, underwater if aquatic) by a character with a succesful healing skill or by a character with healing magic (Cure Serious Wonds or better), then he will recover normally

if this happy event does not take place, the character dies. However, he still may be brought back to life with a Raise Dead(Fully) spell.

Pressure of the deep  

Below the character's racial limit a surface dweller must rest 1 Turn for each period of Turns equal to the character's current constitution or become fatiqued AND suffer 1d8 points of damage per 50 feet over the racial limit by the pressure alone. The spell Pressure Resistance negates this need.
When becoming fatiqued due excertion (like combat) this rest must also be made.
Any character, creature will sense the limit of its race when reached (or the limit the Pressure Resistance spell(s) give).

On itself is pressure above the creatures limit negatable, and not directly important. However when coming from the depth Caisson Disease may afflict the swimmer. When the swimmer (not applicable to aquatic creatures, these have a much higher depth limit and merely dislike the pressure to which surface dwellers have dismay. Aquatic creatures also do never contract Caisson Disease, except when climbing mountains on the surface over 500 feet and falling down , instant or rapid transport) rises more than 10 feet each round coming from a depth over 100 feet, or rises more than 15 feet each round coming from a depth over 500 feet, or when rising more than 20 feet each round coming from a depth over 1000 feet, or when using a Teleportation or similar instant travel, the character must make a saving throw vs paralysis every 50 feet risen  or became affflicted by Caisson Disease. This disease become visible on the surface after about 2 Turns. the character becomes sick, weak, regurgitates, will fall in spasms, his/her constitutionand Strength will permanently be lowered by -2. and they must make each round a saving throw vs paralysis or lose 1d4 hp. This spell can only be cured by a Cure All spell or a Pressure spell(see below) and even then the character must adapt to normal pressure 1 hour for each 100 feet risen. A Create Air spell in an airtight small container (a large barrel will do) with the patient will also remove thee affliction, keeping the same duration.


Sounds are louder and carry away over greater distances, yet the orientation is difficult. The water prevents sound damages. yet distances are multiplied by 10 for normal sounds and by 1000! for high tuned pitches (like whales and dolphins do).


Writings on paper by ink dissolve in 2 turns

Paper will dissolve in 2d10 hours, parchment will loosen up in 1 hour. Leather (including shoes, boots and armor )and other organics will soak up and become hard and brittle when drying later(unless correctly oiled).


The vision on sea or any large water surface is obscured by waves, personal movement, water splashes and blurred in the distance. Underwater (as can be seen by the above table) visibility can be severe limited. To orientate any general direction unless up or down requires the character to survey 1 round  minimal, and a succesful Wisdom and Intelligence check, to get a general feel of direction. Getting lost underwater is a chance of 50%(1-3 on 1d6) and on the surface even 66%(1-4 on 1d6)!! One can always sense the direction of the wind and current without any difficulty (unless totally ignoring these due choice), and this can help maintaining the general direction.