I tried to complete a mission where I had to fix some pipes in the excavation site, and I jumped in the pond with my power armor on. The thing is, I can't swim UP with the armor, and there is no way back to the surface otherwise. I had to get out of the armor to go out of the pond. Did I lost it forever?

No.

You may wanna remove the fusion core. Or u'll need a new frame

It's recoverable once it drains- just fast travel out or there's an elevator that's accessible once it dries up.

You will be sent to that site again to clear out raiders eventually anyways, fighting your way to the bottom of the quarry to get them all.

don't go swimming with PA on. there is one place where you won't be able to get PA back.

Guys it fills with raiders as soon as it drains. There gunna steal his armor

Weeeell I hope there's a way to complete this mission with the guy who asked for it being dead. I uh.. Kinda murdered him. I'm gonna give it a try and let you guys know.

You can still complete it without Sully. You might not get paid, tho. But get the core out of your PA or you'll be fighting it when you come back.

Didn't read to the bottom, so I don't know if this has been said already. But you can walk out, it just takes a while and you have to find the route. Or you can find the elevator on what I believe is the west side? It will take you all the way up.

If you're talking about Thicket Excavations, there's an elevator that works even if the quarry is flooded. Simply find that, get in, and hit the button to go up. If you called the elevator at the top, you'll have to wait for it to come back down, but that's not actually a problem. You could also walk all the way back up, but the route is very long, and you only have a limited amount of air, even in Power Armor, so you're more likely to die if you do that. The elevator is your only real option.

As a general rule, though, you'll want to quicksave before jumping into any body of water when using Power Armor, in case there's no way out.

Nice guys, thanks!!

I wouldn't worry about losing Power Armor....

There are loads more of it just sitting around.

Mirelurk Cakes may offer you some underwater time but yes, there are other suits and frames. You will pass one partial T45 and frame near a pre-war crashed vertibird on the way to Tenpines Bluff. It is in the vicinity of the Robotics Disposal Yard and USAF Satellite Station Olivia. Take a fusion core and either walk or fast-travel it home.

I lost mine on some sort of dam.

It'll be there once it drains. Just be sure to bring another set. You're gonna need it. Oh! And some good firepower.

Someone with jump into it, if theres a fusion core in it

True, so I suggest you dive down and get the power core (as well as the pieces). Just take a mirelurk roast or something like that. That way you'll be able to breath under water for a while.

Another suggestion though. You can still walk up in it when you're under water if you haven't gotten yourself stuck. The platforms and tunnels still exist to get to the metal stairs on the far side of the quarry. It would just take some looking.

Hey in it then fast travel. Happened to me too.