Arizona and California are arguing over Colorado River water again — this time over whether it should be inscribed in law that California can’t take Arizona’s share of river water that’s left in Lake Mead to prop up lake levels.

The dispute is over whether it would benefit the troubled river system to guarantee in writing that one state can’t take another state’s water that’s left behind in the lake — or whether such an effort could disrupt already delicate negotiations over the river’s future.