What is the underground water biome in calamity?

Why is my ocean biome a sulphuric sea biome simultaneously? : r/CalamityMod

Missing Sunken Sea Lab? Spent the last 5 hours trying to find it then used Hero's Mod to show map. Seems to be missing. : r/CalamityMod

Playing on calamity mod. I need to know this biome and what it is please answer fast : r/Terraria

Every Biome In Terraria, Ranked

NEW Draedon Arsenal Labs - Terraria Calamity Rust & Dust World Generation Structures (Update 1.4.5)

I can't find my Sunken Sea biome, any help would be greatly appreciated. I wonder if it didn't spawn because my one underground desert goes all the way to hell. : r/CalamityMod

I can't find my Sunken Sea biome, any help would be greatly appreciated. I wonder if it didn't spawn because my one underground desert goes all the way to hell. : r/CalamityMod

Biome Blade - Calamity Mod Wiki

Terraria Calamity Mage

Why did massive gaping holes form in my world after beating WoF? : r/CalamityMod

Concept art of the Calamity biome expansions: Brimstone Crags : r/Calamitymod_

tModLoader - Calamity Mod, Page 637