Underwater Combat and Pathfinder

I am currently running the Skull and Shackles adventure path for my in-player game.  It is full of pirates, shipboard combat and creatures from the deep.  It also has a good deal of underwater combat situations that make the adventure really differ from a lot of other offerings.  I like the unusual and the non-standard in my games and anything that can make a series stand out for me really grabs me.  When I read the Skull and Shackles near two years ago it was the underwater combat that did this for me as well as the brilliant structure to the adventure path that offers the players substantial steps forward at the end of every module.

After having produced the Pathfinder and Flying Combat post recently I thought it appropriate to look at some of the other fantastical arenas that you can place your battles in the game.  Especially after my players were all moaning about how much it sucks to be underwater in battles at the conclusion of last game.  Good news for them is it will be some time before they have to break out the water breathing spell again!  Underwater combat may not involve the threat of big falls like the combat that occurs up in the blue sky but it really does hamper the player in special ways if they are not natives to the environment.

Underwater combat is offered its own little space in the Pathfinder core book under the environment section which can be accessed here.  Most of the material I include in this post will be recreated from that section of the book, but I’ll give you my understanding of it all.  First of all the thing that you need to understand is how underwater combat differs from combat between two foes on land.  The major point that I found in the battles I have run to date is that unless you have a swim speed, there is no such thing as a five foot step.

The reason that this is the case is to do with the fact the player a) needs to make a swim test each round against a varying DC (with little flow to the body of water I make this a DC 10 check as per the Swim skill description) and that the player must expend more effort to swim a distance of five feet than they would in an on ground combat. In fact if a creature that can move at thirty feet above ground that has no swim speed natively wants to move five feet they would need to essentially use around the full 30′ worth of movement just to travel up to seven and a half feet for their full move!  Therefore there is much more involved in a 5′ step in underwater combat and doing so would trigger an attack of opportunity.

Underwater combat image showing woman underwater
Underwater is a whole new world. Image by Michael Vincent Manalo, legalese at bottom of page

One thing you also must consider when dealing with the underwater environment (not just in underwater combat though it becomes very important there) is the idea of how you breathe there.  If you are intending a sojourn to the underwater realms you will want a spell caster loaded up with the water breathing spell, or a bunch of potions that are all labelled the same.  If you can’t have that the details of how long you can hold your breath for is located in the Swim skill rules and let me tell you that it is not very long.

Underwater combat and vision

There are some other considerations that you must address too.  Pathfinder is very easy on the visibility rules in water.  In a “clear” water environment you are looking at around 4d8 x 10′ vision (up to 320 feet or 96 metres is HUGE underwater) and murky water offers you 1d8 x 10 feet (up to 80 feet or 24 metres which is MASSIVE).  I do not think that these ranges are very accurate to real life visibiliity that I have experienced as an avid swimmer in natural areas, especially the murky water version and I am more than likely going to reduce that to about 80′ in clear water unless looking down to the sea bed if it is shallow gives a longer range and maybe 10′ in murky water which is still generous!  But play it by the rules if you prefer.

Now, the players in my game are sneaky and tricky and it has not happened yet but I am sure they are thinking about the possibility of using invisibility underwater to get past something.  Well, it is not that easy.  As described in the book invisibility actually makes a section of water appear with a large bubble the same shape as the invisible figure in it!  It negates the effect of not knowing where the invisible creature is and reduces the 50% miss chance to a 20% miss chance in underwater combat.

Fighting underwater

One thing that the players need to understand is how incredibly hard it is to fight underwater if they are not geared for it.  The underwater combat table below spells out the rules (table recreated from the PRD) and it shows just how difficult it is to conduct underwater combat without the proper preparation.

Condition Attack/Damage Movement Off-Balance
Slashing/Bludgeoning Piercing
Freedom of Movement normal/normal normal normal no
Has a swim speed -2/half normal normal no
Successful swim check -2/half normal quarter or half no
Firm footing -2/half normal half no
None of the above -2/half -2/half none

As you can see there are several options to look into when you are preparing to fight in underwater combat.  The top of the table is the best option being that the Freedom of Movement spell allows you to essentially ignore the fact that you are underwater and everything functions as normal.  If you have a swim speed this is also the same apart from the fact that if you use a bludgeoning or slashing weapon it is harder to hit with and does less damage so gear up with your piercing weapons.  A successful swim check is the same except if you want to move you can only move a quarter of your normal speed or half if you take a full round action, thus negating the ability to strike out after moving.  If you have a firm footing on perhaps the rocky sea bed or the hull of a ship then you are OK as well and can move up to half your speed.  The final line of this table is altered from what appears in the core rule book.  If my players fail a swim check then they can not move.  In the table on the PRD and in the core book they have “normal” listed in the movement section and unless I am missing something, I feel that may be erroneous.

My house rules

To continue with my own house rules I make my players make their swim check every round and if they fail they are in no position to attack, move or cast a spell as they are flailing around trying to maintain control.  The official rules above really suggest (apart from the negatives to piercing) that there is no real difference if you make the swim check or not (and if I left it as normal in the movement it would be better!).

Other rules like spells, ranged combat and land to water combat

Underwater combat has a few other considerations to take in.  First is spellcasting while underwater.  If you can’t breathe underwater (holding your breath) then you need to make a concentration check to get a spell off with a DC of 15 plus the spell level.  Ranged attacks underwater suck too.  Using any ranged weapon in the water reduces its range attribute to 5 feet.  That means for every 5 feet away the target is you take a -2 penalty to your shot.

Say someone is on the deck of a ship and they are attempting to shoot you when you are in the water.  The good news is that you get a +8 to your AC and if they loose a fireball or something similar you also get a +4 to your reflex saves!  Speaking of fire, how does it work underwater.  Well, the first thing to understand is that non-magical fire does not.  I would actually count alchemist bombs in this as well but I am not sure if that was clarified anywhere.  I know alchemist’s fire definitely does not work.  If the fire is a result of a magical effect like the aforementioned fireball then the caster needs to make a DC 20+ level of the spell caster level check for it to work.  The spell does not appear as fire but as boiling water or concentrated steam as is your whim.


So there it is.  For a player it sucks to be in underwater combat.  That is something that you really need to consider when you are designing your encounters too.  I would tend to drop the CR levels of encounters down a peg or two as there is just an inherent difficulty with underwater combat until the players get into the mid-range and gain access to freedom of movement spells or rings.  The CR levels of the Skull and Shackles campaign seemed to be a bit lower in these sections as opposed to encounters on land and I think that is the reason why.  I know once my players read that they are not going to be below the waves for a while that they will breathe a huge sigh of relief!  I hope my discussion of the rules here have offered up the idea to run some underwater combats.  It is a great place to hold combat and offers up some really different encounters to pique the interest of your players.  Until next time, keep rolling!

Image created by Michael Vincent Manalo and included here under a Creative Commons Attribution – Non-commercial – No derivative works 3.0 licence

1 Comment

  1. Great article!

    I would add a house rule saying spells with a verbal components cannot be cast normally underwater. Even if the caster is benefiting from the water breathing spell, the precise sounds necessary for spell casting just can’t be reproduced correctly in that environment.


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