If California and Oregon Have a Conflict Over Water Usage

If California and Oregon have a conflict over water usage, how does the matter get settled?

A) The two states go to war and the winner decides how the water gets used.
B) A neutral state, such as Oklahoma, makes a binding decision that California and Oregon have to accept.
C) Past water usage records are examined and each state is granted their average usage over the last decade.
D) The federal government decides.
E) Switzerland, due to its reputation for neutrality, issues a binding resolution.