Does a swim speed let one breathe water?

[magispitt]

As per the title - I'm making a 3rd level aquatic druid for Skulls and Shackles and am looking at the "Heart of the Sea" alternate trait for humans. The aquatic druid already gets a swim speed, so I'm wondering if the ability to hold one's breath twice as long is a waste.

[Melkiador]

Just having a swim speed doesn't give you water breathing. But polymorphing into a creature with a swim speed does.

[BigNorseWolf]

a swim speed only comes with the ability to breathe water if its from a polymorph effect.

[Oddman80]

What if you polymorph into a dolphin or a whale?

Neither of those creatures have the ability to breath under water, and the Hold Breath (Ex) ability is not granted by any of the polymorph spells as far as i can tell.

[Melkiador]

If you polymorph into a dolphin, you can still breath water. Because magic. It's not like you actually become a dolphin. You just get magically changed into a form that resembles one. And you magically gain some abilities related to that form.

[My Self]

Swim speed and water-breathing are independent. Note how the Kineticist's Waterdance (Slipstream) effect and Greater Waterdancer (Water breathing) effects are separate. Swim speed does not necessarily grant you the ability to breathe water.

As for polymorph, you should be able to breathe water when you change into a water-breathing creature. It's sort of messy, but Polymorph is designed to give you stats and special features in a less-than-broken way (i.e. actually getting all the stats/special features of the target creature). A common sense ruling would say yes. A more in-depth RAW reading isn't something I'm going to dive into right now.

[Mysterious Stranger]

Having a swim speed does not grant anything else expect the abilities listed. There are plenty of animals that have a swim speed but do not breathe water. Beavers and seals are probably a better example than whales and dolphins. This is also backed up by the aquatic druid archetype They gain the Seaborn ability at 9th level, which among other things grants them the aquatic type and the amphibious trait. If just having a swim speed was enough to breathe water then they would not need this ability.

There is one exception to this which is what may have caused the original poster to think that a swim speed grants water breathing. A polymorph affect that grants a swim speed does in fact allow the character to breathe water. So the druid who changes into the form a beaver can breathe water, even though a real beaver cannot.

So once your druid reaches 9th level the ability to hold your breath for twice as long becomes less relevant. It is not completely useless because it may still come up in other things like poison gas or being suffocated.

[Aristophanes]

If you want to play a druid that breathes water, play an Undine, and take the "Amphibious" alternate racial trait. I gives you a swim speed equal to your regular speed, and enables you to breathe water.