Kachi Mayu (Quechua kachi salt, mayu river, "salt river", hispanicized spelling Cachi Mayu) is a Bolivian river east of Poopó Lake in the Oruro Department, Challapata Province, Challapata Municipality. Its source, the Jach'a Juqhu River, is considered the origin of the Pillku Mayu. There is another river of the same name, Kachi Mayu in the Oropeza Province of the Chuquisaca Department, which is a left tributary of the Pillku Mayu.