Good Alligned Undersea Monsters?

[Yakmala]

So, with Saltmarsh out, I had an idea for a Celestial Warlock with a Sailor/Fisherman/Shipwright background. He somehow managed to help/save/attract the interest of a huge undersea beast and in gratitude, the beast became his patron and granted him some of its power.

The question is, what creature could this be? The majority of really powerful undersea creatures are evil, or at best, neutral. Can anyone think of any good aligned beasts, either from undersea or perhaps the elemental plane of water, that would fit the bill?

Some ideas that occurred to me:

1: Baby Kraken. It's still young enough that it hasn't developed it's evil tendencies yet.

2: Dragon Turtle: They're typically of average intelligence and neutral in alignment, but I could envision a particularly ancient one that exceeds expectations.

3: A good aligned Marid: Not really a beast but might fit the role well.

Any other suggestions?

[Monster Manuel]

What about a Bronze dragon? Not explicitly aquatic, but they can breathe underwater and are described as loving the sea.

I've never seen one actually used as anything, but an Empyrian could work, if it was the child of a Poseidon-like Sea god.

You could also consider a Storm Giant Quintessence; not really a beast that could be rescued, but it does fit as the sort of thing that might become a patron.

I'd be careful about writing in the "saved my patron's life" bit into the backstory...it could be fun, but hard to justify how something that's powerful enough to act as a warlock patron would need to be saved by a low-level PC. Maybe the bronze dragon was shapechanged into a porpoise in order to watch a ship that had piqued its curiosity, and got tangled up in the lines. It could have easily changed back and freed itself, but in the process would have destroyed the ship and drowned the crew. Your character saw the tangled porpoise and rescued it, saving the dragon a huge headache, and so it agreed to become your patron.

Something like that?

[QuickLyRaiNbow]

It could be a dragon - some of the good dragons are aquatic. Any water creature, including a kraken, could be a servant of Ben-Hadar, Prince of Good Water Creatures.

[Thorgrim]

Baby Krakens are evil according to Saltmarsh, but you're of course welcome to refluff.

One thing to consider is that the Celestial patron is, well, a celestial. They seem to be pretty uncommon under the sea, but perhaps there's an opportunity to save a trapped or cursed angelic being of some kind (chained to a sunken ship or polymorphed into a fish or similar).

[Grek]

What about an aquatic Empyrean? The child of some sort of sea deity.