The Sulphurous seas is near Splatsville, It's a sea that is full of Sulphuric acid. The Sulphurous sea used to be a regular ocean with a city near it called Sulphur city, during the False Republic War, a leader named Damien burned Sulphur city to the ground, after the False Republic War when the ice caps were nuked and the ocean levels rised, a sulphuric acid waste from the ruins of Sulphur city was swept away. Once the seas receded and the land came back, The Sulphurous seas was made.