The Great Flood was the end of a planet-wide ice age on the planet Kamino, occurring in 19,000 BBY. When the ice melted, the water levels rose tremendously and submerged most of the world underwater. It also lead to endless storms, and it sank multiple cities underwater. The Kaminoans were only able to survive because of their supreme knowledge of genetics. They then started living to great ages, and few knew about Kamino.