Thalassophobia-(Into the Abyss)

This modpack is designed to instill thalassophobia in anyone who plays it, with monstrous creatures lurking in the depths of the ocean. 

There are mods that add sea monsters, and there's also The Man From The Fog and From The Fog, so you don't have to flee the terror by taking refuge on islands. There are mods that add much more content to Minecraft's oceans, mods that improve the quality of life and the vanilla experience, SecurityCraft to defend yourself against stalking creatures, and a variety of other mods that add physics to the water, etc.

If you want a better and more unforgettable experience, install OptiFine to add the shaders that come with the modpack (the complementary shaders), and replace the Physics Mod with Physics Mod Pro, which is the mod that adds physics to the ocean. It's free; you can find it on the creator's Patreon by searching for it on Google. Remember to install the version for Forge 1.20.1.