the aqueduct enters the o'neill forebay reservoir west of volta, where water can be pumped into a giant offstream storage facility, san luis reservoir, formed by the nearby b.f. sisk dam. san luis reservoir is shared by the swp and the federal central valley project; here water can be switched between the california aqueduct and delta-mendota canal to cope with fluctuating demands. the swp has a 50 percent share of the of storage available in san luis reservoir.