Circa 4400 BC, radioactive debris from an ancient supernova passed through Bwuja's star system and incinerated the planet's surface, wiping out Bwujan cities and boiling the seas. Having witnessed the debris approach in the sky for centuries, a small portion of Bwujan civilization with gill transplants were able to survive the extinction event by living in deep trenches below the ocean.
Over time, the surface cooled and gill mutations gave the Bwujans natural water-breathing ability. Their civilization advanced to the building of submarines and cities with strikingly tall buildings along the ocean floor. By the 23rd century, the radiation had dispersed.
In 2266, the Federation starship USS Enterprise was assigned to study how the genetic mutations affected Bwujan culture, with Urey University xenobiologist Barbara McCoy sent to direct the mission. A landing party visited the undersea civilization using comp-ox capsules to breathe. They discovered isolated groups of air-breathing Bwujans trying to survive despite the efforts of local priests, who considered them spawns of the devil. Eventually, water-breathing royalty adopted the water-breathing son of air-breathing parents, while those parents agreed to raise the king and queen's air-breathing son. (TOS comic: "The World Beneath the Waves")
- Undersea cities
- Above-ground village