The Zhamaja: Wyrm of the Abyss (5E)

From publisher blurb:

Foul, alien things that prowl the sunless depths of the ancient underground, zamaja are terror-inducing predators who are as comfortable gliding through subterranean seas as they are burrowing through the earth. Originating from somewhere just beyond space and time, these aberrations arrived millennia ago in waves that, lacking any way to adapt to the sun-filled world, would have died off had they not migrated to the subterranean world they now call home. Having long ago adapted to the dark, these worm-like monsters prefer underground bodies of water – especially when those environments feature salt and limestone deposits, both of which are mild intoxicants to them.