Along with the sound of the discharge warning siren, a declaration roars: "Open the dam's gates!" This is an epic story about building a dam to resolve a water shortage in another world.

The water of the vast Holy Valley River has disappeared...?! William Parthenon, a reincarnated person and dam engineer, meets Caliba Acombo, a mage; Archana Hoover, an adventurer; and Gravy, a swordsman. Together, they rise to face this difficult challenge!

The incident begins with the suppression of the rioters who were fighting over the water supply. While suffering from amnesia, William volunteers to be the guard to investigate the local water conflict. During his investigation, he deduces from the shape of the stones in the riverbed that there must be something drying the water up. The party heads for the headwaters where the water spirit, Undine, lives.

All for the sake of delivering the blessing of water to the people! This is a unique Dam x Isekai fantasy!!