The Sea replaces any aquatic nature gods in your world, because it is the ur-concept, the living embodiment of itself, because it is itself.
It would be foolish to think of it as anything else, but men do.
Some think of her as a treasure-keeper, a goddess of horizons because she alone can touch the distant sky, and she alone binds the earthen parts of the world, her flexible strength mightier than that of stone. Always with the promise of something new, something unseen, something unknown. Something precious, something dear. Promises, promises. But nothing is free.
Some think of her as a sister to the moon, their cycles of rising and falling, ebb and flow not synchronistic, but so very close, how could they be anything but related? Would that the Queen of Night step forth from her home, certainly her silver-lined hem would be made of sea-foam, whitecaps spun with starlight to gossamer fringes that sing of summer nights on the open sea, the heavens above revealed in all their glory while her glass-still reflection drinks deep of the sky like a mirror. And how she comes alive when the sun rises and sets, her own attire changing to match the tropical wine glows and gilded rays that burn like god-gold from the heavens. Certainly her beauty is incomparable to anyone else’s, and some chase that, fear spotting their eyes with tears as joy and peace takes their soul in a manner no human dress could.
Maybe the most apt comparison is to a bride, which is why sailors use female pronouns to describe her, and say that they are “married to The Sea”. Certainly, it would give credence to their belief, however wrong or right, that women are bad luck underway. Those forever tied to the sea would say that she is a jealous lover, and that any attention shown elsewhere in her presence would draw her ire. That thing they do fear, and speak of in hushed tones.
They’ve seen her split a mast with a thunderbolt, and splinter a hull with a curl of her saltwater hands as effortlessly as a maid wringing a rag free of the dirt that plagues it. They’ve seen her mood change with a breeze, some little slight provoking her wrath, and prayed forgiveness and mercy from her horrors, only to return to her after the briefest stays ashore. They’ve seen the faces in slate-grey waters of freezing liquid iron, pale and ghastly staring back at them. Because what The Sea takes, she keeps.
Those that sink below are not given the respite of paradise, nor are they doled out their just-desserts in the underworld, nor sent to moil in some purgatorial limbo. Theirs is a fate far worse than death, for they join the ranks of that morbid locker they call The Deep. For what purpose could she call them there? Why keep them at all? Sailors ask not, and wonder not, lest they go mad.
Only fools would try to steal from such a thing as powerful, or as fickle.
But some they say have. Or perhaps, more accurately, she has allowed. A young man weeps at the docks as his lover departs, his tears pure and meeting the sea. He will always return to him, even beyond the Veil. A young woman picks up a shell on the shore, an early dowry for her sailor son. A warrior rinses blood from his hands by the tiller, and the goddess below him drinks it like wine. He will never be defeated on board a ship, so long as he pays tribute. An old captain knows the waters around the rocks with preternatural grace, and years from now when his heart stops he will fall into the arms of his beloved one last time. They dressed in mens’ clothes to work the rigging, and fell in love with one another again under strange stars. Their love will leave a wake of blood and bodies overboard as they chase the gold promised on the map, never knowing who blessed them with it.
There is no formal church to The Sea. No ritual worship. There are only sailors, and land-lovers. Those who have seen her beauty, danced on the waves, or tasted her sea-spray kiss and yearned for more. This is because The Sea is The Sea, and it is itself.
It has always been, and always will be.