Just a reminder of Tressa the Red's speech to you:
Ah, Welcome. Sorry about all of that. Part of the rub, you know. Comes with the house. I haven't found any way to turn it off. Congratulations on getting through it-no one else has yet. Except me, of course. How can I help you?
Yes. I know. It seems there's a leak. Between this world and this "Earth" you visitors hail from. I can only imagine it is the work of the Sea Hags, but I can't be sure as there's so much magic around the Devil's Cross-that I can't quite pick that out.
If it is their dark magic, elemental sorcery can't counter it. The two forces just don't mix. The only way to cancel one of their spells is to destroy them. Even that won't return Caribdus to the way it was-I don't know any way of doing that-but it should stop the leak and put an end to their terror at the very least. I've actually been slowing down the leak by treating they symptoms instead of the disease, so to speak, but it's trying work. Doesn't leave me with much to go out and actually try to fight the hags. Plus, if a whole Kraken fleet and over 50 archmages couldn't do it well...
I don't suppose you've got any carroway fruit do you? That stuff is great for restoring my energies.
Anyway, I've put together the first piece of the puzzle. Seems their black magic is all about weird rituals and so forth. A glass of water from another world poured of the Devil's Cross makes the witches come out of the sea. That's not such a great idea though because I suspect they'll arise as gargantuans as they did against the Kraken. You'd need some mighty powerful magic, maybe some ship's cannons, to take them down.
You can probably find water from another world on one of the wrecks that didn't make it out of the Flotsam Sea. For it to summon the hags you have to pour it over the ruins of Ograpog and speak the witches true names. I'm afraid I haven't met anyone yet who knows them-so many people from Ograpog died in the flood it's difficult to find anyone who knew them or witnessed their trial. I know. I've tried.
There is one thing that might help, though. There's a relic called the Tears of Lys. It's a gem said to grant visions to those in need. It's possible the device could tell you the witches true names. Last I heard it was in the possession of a cute fire mage named Tomas de Orinjo. Tomas serves aboard a privateer working in and around the Gray Isles. I don't know what it would take to make Tomas part with the relic though. Such a thing is nearly priceless.
Now, go save the world, handsome.