- Everyone can swim at ½ their movement rate
- Treading quietly or in combat use dungeon speed
- Swimming quickly use wilderness speed
- Creatures can dive at 2x their swim movement speed
- Maximum load to ascend/tread in water is 20 lbs (200 coins) plus an additional 10 lbs (100 coins) per +1 Strength bonus
- Exceeding a maximum load causes a character to descend at a rate of 5 feet if they are trying to stay afloat or 10 feet if they are allowing themselves to sink
- Creatures can hold their breath for 1 minute (6 rounds) plus an additional 2 minutes (12 rounds) per +1 Constitution bonus
- A character has a 1-in-6 chance of drowning the first round it remains submerged after its air runs out. Each subsequent round increases its chances of drowning by +1 (2-in-6, 3-in-6, etc)
Vision, Hearing and combat
- Humans can see a maximum of 200 feet in perfectly clear water. For most “normal” bodies of water (i.e. lakes, seas, etc) reduce this to 100 feet. Especially murky water could reduce vision even further or even effectively blind
- Sunlight only penetrates to a depth of 100 feet, beyond which a lightsource is required. Infravision is reduced by half
- Without magic humans cannot communicate underwater and listening is impossible
- Swords, axes, clubs, maces and similar weapons that require the force of a swing deal reduced damage (d4) and only apply half of the wielder’s strength bonus rounded down
- Spears, tridents, and other piercing weapons that rely on thrusting deal regular damage. Throwing these weapons reduces their range by half.
- Crossbows and bows deal reduced damage (d4) and have their ranges reduced by half. Slings are not usable underwater.
- Combat occurs both on a horizontal plane and a vertical plane. As such players are encouraged to keep track of their depth each round.
- Aquatic creatures surprise characters when they are at least half submerged in the water on a 4-in-6
- Swimming, even treading water, always counts as movement. During an attack a character will sink 5 feet
Example of Play
Ref: You stand on the edge of the cavern, dark black lake below that reflects back your torchlight as if it were a mirror. A little further out you see a soft white glow in the inky depths that is not a reflection of your torch, it is something else.
Player 1: Do I see anything moving?
Ref: No.
Player 2: Someone should tie a rope to themselves and swim down there to see what it is. How deep is it?
Ref: Hard to say, probably no more than sixty feet.
Player 3: Not me.
Player 2: I’ll do it. I take off my armor, tie a rope around my waist, and put my dagger between my teeth before jumping in.
Player 1: I’ll hold the rope.
Player 3: I’ll be the lookout. And watch you die.
Ref: You plunge into the icy subterranean lake and you quickly realize you can’t see anything.
Player 3: I cast Light on his dagger.
Ref: Now you can see that the water is as clear as it is cold. You don’t see anything below you except the faint light much deeper in the lake. It is probably 60 feet down and about 30 feet out. You can swim 20 feet per round, dive 40 feet per round, and hold your breath for 10 rounds.
Player 1: He’s in rounds?
Ref: Yes.
Player 2: I swim out until I am over the light-
Ref: 2 rounds go by -
Player 2: Then I dive down toward the light-
Ref: 1 round goes by, then you are within 20 feet of the light and realize it is a giant unblinking phosphorescent eye in the middle of a huge fleshy pale starfish. 9 rounds of breath.
Player 2: I start swimming back up.
Ref: (rolls d6… 3) Just as you turn to begin swimming back to the surface you feel a sharp pain in your leg and a 5 foot black scaly fish with yellow eyes tries to drag you away. 8 rounds of breath.
Player 1: Do I feel that on the rope?
Ref: Sure. The rope tugs hard. Roll for initiative, (rolls d6… 1) you go first.
Player 3: I’ll help pull him up.
Player 1: Yeah we are both pulling him up as fast as we can.
Ref: One of you make a strength check, 2-in-6 but I’ll make it 3-in-6 since both of you are pulling on the rope.
Player 1: 5.
Ref: You feel the rope burn your hands as something tugs back.
Player 2: Crap. What do I see?
Ref: There are three man-sized black fish with sharp scales, yellow eyes, and teeth like needles. One of them still has your leg. You would have to make a strength check, 2-in-6, to break free to move.
Player 2: Since it is holding onto me can I stab it?
Ref: Yes, THAC0 -2 since its holding onto your leg which makes it easier to stab.
Player 2: I rolled a 17.
Ref: You stab it in its big stupid yellow eye.
Player 2: 3 damage.
Ref: The other two fish swim past in quick lunges but both miss. The one still holding your leg in its jaws drags you deeper, past the unmoving starfish. You are now 40 feet out and 60 feet deep. You are literally “at the end of your rope.” 7 rounds of breath. Roll initiative again, I got a 4.
Player 1: 5! We will try to pull him up again.
Ref: 3-in-6 again, but there is no more rope so if you fail you need to choose to either let go or on the fish turn you will end up making a save vs. death to not be pulled in.
Player 3: We pull! I’ll roll… 6! Oh no…
Player 2: I’m going to try to escape this time! I rolled a 3! You said I needed a 1 or 2?
Ref: Yes. The fish tries to take you deeper almost as if it is trying to keep you away from the other two fish that are prepared to give chase. I need a save vs. death from both of you holding the rope.
Player 3: 15! I made it!
Player 1: 10… I did not.
Ref: [Player 1] topples into the lake as the rope yanks hard. [Player 3] Lets go just in time and watches the heavily armored fighter topple into the underground lake along with the rope.
Player 3: I only have Charm Person, Invisibility, Web and Fireball memorized. I’ll watch hopelessly.
Ref: One fish chases [Player 2] and the other fish wheels around and heads directly for [Player 1] that just crashed in the water. [Player 1] you have 18 rounds of breath. [Player 2] you are now 90 feet deep and 60 feet out. You have 6 rounds of breath. Roll initiative, I got a 3.
Player 1: I also got a 3-
Ref: You win ties, go!
Player 1: I am wearing plate, can I even swim?
Ref: You can swim but you will sink 5 feet deeper every round. If you let yourself sink you will sink 10 feet.
Player 1: Can I see a shoreline that I can climb up?
Ref: No, the cliff [Player 3] is standing on is only about 5 feet high but it's wet and sheer. To your left and right the water extends into oppressive darkness.
Player 3: Can I lower my staff for him to grab onto?
Ref: Sure. 2-in-6 to get him up, on a 6 he’d pull you in though.
Player 3: 6… I don’t even get a save?
Ref: Sure, if you make it your staff slips out of your hands. If you fail, you fall in the water.
Player 3: 13! Made it!
Ref: [Player 1] you are now in the water, sinking, and holding [Player 3]’s staff.
Player 1: I let go of it, draw my sword, and get ready for this overgrown fish to come get me.
Ref: Great, you are now 10 feet deep and have 17 rounds of breath. You can make an attack on the fish that is closing in.
Player 1: 20! BOOM!
Ref: Super! Roll 2d4 and add half your strength modifier.
Player 1: WHAT?
Ref: Not easy to use a sword underwater.
Player 1: 9 damage! Eat that!
Ref: Nice! [Player 2] what’s your plan?
Player 2: I’m going to try to escape again and start swimming toward the surface. I rolled a 2!
Ref: Whew! You kick free and start swimming straight up. You are now only 70 feet deep and you have 7 rounds of breath. The fish that you kicked free from (rolls morale… 8) shakes a little and swims off into the depths apparently uninterested in prey that is willing to fight so hard. The one that was chasing whooshes past you in the black. [Player 1] The fish you sliced open also turns tail and follows the others into the dark depths. We are out of combat for the time being, but will not yet be leaving rounds. You have 16 rounds of breath. [Player 2] it takes you 4 rounds to get back to the surface, you have 5 rounds of breath so no drowning check needed.
Player 2: That was close!
Ref: It was, but [Player 1] is still sinking.
Player 3: I drop my stuff-
Ref: It takes a round to get as much off as you can that would be ruined by water. [Player 1] you sink another 5 feet and are 15 feet deep. You have 15 rounds of breath.
Player 3: I dive in and help [Player 1] get to the surface.
Ref: Done. Everyone is back at the surface, [Player 2] and [Player 3] help [Player 1] stay afloat. The cavern seems immense and there is no beach insight. The magic light from [Player 2]’s dagger is a lonely pinprick like a solitary star in a dark sky. The low cliff face seems unscalable due to its sheer surface, wet, and mud.
Player 2: I can climb it. 34!
Ref: Well done! It takes a turn to scrabble up the wall and get both [Player 1] and [Player 3] up. You are back where you started. In the water you still see that pale glow.