The History of the Zora, Part Two is a Monument, and a location you need to visit for the quest Zora Stone Monuments.
A Reservoir of Hope as told by King Dorephan.
Once every 10 years, the Lanayru region experience unusually heavy rainfall. The Zora River flooded every time. The tides damaged not only our domain but our people, washing away pour souls and causing great suffering and disarray. The Zora king of that time, after seeking aid from the king of Hyrule, rode out to see what could be done. By joining the architectural genius of the Zora and Hyrule;s technological prowess, East Reservoir Lake was swiftly built. Thanks to this fruitful partnership, Hyrule was no longer plagued by these devastating floods. In gratitude, the Zora king promised the king of Hyrule to manage the reservoir level to protect all of Hyrule from floods. Each Zora king since has kept that oath, spanning 10,000 years. That is why the serveroir signified our bond with Hyrule.