Oasis de la Sierra El Pilar. 02/02/2008; Baja California Sur; 180,803 ha; 24° 43' N 110° 54´ W. Located in the western slope of Sierra del Mechudo, this site is composed by numerous oasis which are of great hydrological and biological importance, supporting unique fauna species such as the Peninsular clingfish (Gobiesox juniperoserrai) and the Killifish (Fundulus lima), both considered endangered. This oasis represent very fragile ecosystems, mainly affected by natural causes such as extreme draughts, and human activities including unsustainable agriculture and livestock. Among the main threats that negatively affect this site are: the presence of invasive fish species (Tilapia cf. zilli, Poecillia reticulata, Xiphophorus helleri and X. maculatus) and plants (Cryptostegia grandiflora); the construction of hydroelectric power stations to use water from the springs; and the use of biotic resources without a management plan and control, such as illegal hunting and extensive livestock of ungulates.