Adult fantasy, heroine has ability to recognize magical artifacts, which are illegal and dangerous; magical "weir" periodically disrupts ocean travel, heroine and male partner end up being turned into sea gods

[Mike]

Picked up this book at random during a trip years ago and have never been able to remember title or author. The woman is caught with one of the illegal artifacts, which I believe is why she gets sent out to sea during the weir's dangerous appearance, supposedly to be transformed into something monstrous, finds herself and her lover instead transformed into powerful beings (though still kind of monstrous). I believe it was one book in a series. Anyone got a clue?

[Kris]

Mike, around what year did you find this book?

What does a "weir" look like?

What are the main characters' jobs?

Is this set in a medieval-type fantasy world?