A multistate agreement aimed at shoring up Lake Mead can’t be finished until California finds a way to solve two major, long-simmering environmental fights. That was the message from top water managers Thursday gathered in Las Vegas for the annual conference of the Colorado River Water Users Association. For the past 18 months, Nevada, California and Arizona have been negotiating a drought contingency plan to keep Lake Mead from shrinking enough to trigger a first-ever federal shortage declaration and force Nevada, which receives most of its water from the Colorado, and especially Arizona to slash their use of river water.