Operation: Overkill II

The Earth's water supply tainted through generations of heavy industrial contamination, the remaining quantities of unspoiled drinking water were converted into stable water crystal form. Planetary defenses weakened in this time of environmental catastrophe, we mounted a valiant but ineffective defense against the water-crystal-seeking extraterrestrial Hydrites, led by their brutal general Overkill, in a conflict that reduced human civilisation to a few obscure overlooked outposts and turned our remaining ecosystem into a radioactive wasteland, rife with tunnels and ruins and a fecund breeding-ground for disease, mutants and abominations.