Deluge
From Halo: Daybreak
Deluge, formerly known as Jart, is a Covenant waystation and trading world in the Jartuub Salient. A former Sangheili colony, a planetary flood initiated by an increase in stellar activity and consequent glacial melting half a millennium ago caused the majority of the original inhabitants to abandon the world. Most of Deluge's cities from the original era of settlement now lie in ruins, partially or entirely submerged. At least two of the semi-flooded cities have since become a haven of trader and pirate activity, and many Kig-Yar in particular call the planet home. The capital city in particular - which now carries the same name as the planet - is a nexus of activity, and a ramshackle of structures has been built on top of the foundations provided by the city. Some of the towers and domes remain partially above the water, and many bridges and pontoon-structures cross between the "islands" created by the partly submerged spires, complemented by the husks of scrapped ships of both the space- and seagoing kind.