One of the two underwater cities Merrthis is home to the Merrid people, as they are commonly referred to. The Merrid people are made of a mix of Kuo-Toa, Merfolk, and Merrow. Marrthis was founded shortly after the flood. The races that came together were ones that were generally ostracized prior but they saw the flood as their chance to make a new life for themselves.
Tsunatia
Like Merrthis, Tsunatia is the other underwater city. However, unlike Merrthis that was founded post flood, Tsunatia had existed prior to the flood. The Tsuna people are comprised of Water Genasi, Tritons, and Sea Elves. The general demeanor of the Tsuna people is an air of superiority. They view themselves as the superiors of Thalass due to their amphibious nature and the age of their culture. They also specifically despise the Merrid people seeing them as a gathering of monstrous races that pollute the waters.