So pulling the hood up and down takes an action - but why would you ever put the hood down?  Can you only breath water when the hood is up?

If the hood is down, you don't get the benefits of the cloak until you use an action to pull it back up.

A character would probably pull it down for role playing reasons, since someone with a hood constantly pulled up would probably seem suspicious.

Also, the DM might rule that, because your hood is pulled up, you are limiting your peripheral vision, thus causing penalties to your Perception checks.

Thanks for the reply.  Those are good points and make sense.  To be clear, one other thing I was asking was essentially "if the hood is up, can you breath only water and no longer breath regular air until the hood is down".  This would imply that you'd need to hold your breath if the hood was up and you were outside of water, and it would make a strong incentive to not pull up the hood until you were ready to do some swimming.  For now, I'm ruling that you can still breath normal air while the hood is up, but my players initially assumed they could not, so I thought other people might have the same assumption.

That's actually a really interesting point, but I believe that you can still breath air like normal due to that the wording is "you can breath" and not "you breath" or "you can only breath".

That wording is kinda funny though, might make for an interesting cursed version of the cloak where you have to have it down to breath air.

"It takes an action to raise or lower the hood"

What kind of nonsense is this? "Hang on guys let me take the better part of 6 whole seconds to put my hood up"

Feel it's more that it takes those few seconds for the magical effect to activate or deactivate when you put the hood up or down.

If your a rouge or dont mind looking shady or in my case are already not trusted it shouldnt matter. Another point would be if your stats are like mine you wouldn't be rolling perception checks especially if you have the berserker ability that makes it where you cant be surprised. One last thing is why not make it a bonus action to activate/deactivate the effect.

uh, style purposes

My assumption on why it would take an action instead of bonus action is because something similar to Mortimmer stated. Maybe once the hood is up either a bubble is created inside the hood similar to The cap of water breathing. Or maybe it takes a second to make gills grow from your neck. Another reason I could see it is if you are in combat and get thrust into water and constricted by say a kraken or some other tentacle monster. It would take away the drowning affect of something trying to constrict you and drown you for a turn.

So if a character that already has a swim speed like a triton or a fighter with the mariner fighting style wears this cloak, does it add an additional 60 ft of swim movement or just make the swim speed 60?

So does the existence of this item make the Cap of Water Breathing obsolete, particularly for Artificers who can create both? For a while I assumed this needed Attunement, but it doesn't so... Why bother with a Cap of Water Breathing?

that would make sense, i dont think it would take up a whole action to do that, maybe a bonus action

so your telling me, that a dwarf can swim faster than he or she can run, because they're wearing a piece of clothing that if it weren't magic, would just weigh them down?

@AladrakeAurix: the wonder of magic items :-)

My interpretation is that the manta ray tail that is part of the cloak is what allows the character to propel themselves through the water at this speed. The dwarf doesn't need to just rely on kicking their short legs for propulsion. 

...and what about someone using this over Plate Armor?  Let me just jump into the water and not drop like a rock to the bottom anymore...?

The joys of magic!

Say you are setting up a campaign where players will need to breathe underwater, and this might appear in a magic shop. What would a good price point be? Level 6 players

Online magic item generator puts the price at 6,000GP. Not sure if that helps.

You can breath, yes. However, can you still talk?