The Metropolitan Water District of Southern California on Tuesday sealed California’s participation in a landmark Colorado River drought management plan, agreeing to shoulder more of the state’s future delivery cuts to prevent Lake Mead from falling to dangerously low levels. With California signed on, the plan can move to Congress, which must approve the multi-state agreement before it takes effect. The MWD board took the step over the objections of the Imperial Irrigation District, which holds senior rights to the biggest allocation of river water on the entire length of the Colorado.