The rules governing the Colorado River were made for a ‘previous world’ and the West is now confronting a 21st century nightmare as it runs dry

The Colorado River is in dire straits, and as it becomes clear that the river does not have nearly as much water as it once did, states that have relied on it for over a century are fighting over what remains.

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On Tuesday, government officials from the Department of the Interior released a draft analysis with ideas on how to slow the Colorado River’s depletion. It provides freshwater to 40 million Americans and is the eventual meeting point of waterways in a massive area of around 246,000 square miles, but climate change and overuse have shrunk the river drastically over the past few years. Its flow has dropped 20% over the last century, and drought last year left two of the river’s largest artificial reservoirs, Lake Powell and Lake Mead, at under 30% capacity.

Seven states—Colorado, Utah, Wyoming, New Mexico, California, Nevada, and Arizona—count on the river for water. The government proposed three measures to halt the decline of the river’s water flow affecting the three so-called Lower Basin states—California, Nevada, and Arizona. Water supply for the four Upper Basin states would not be affected by any of the proposals.

The first option is to do nothing, which could lead to a situation known as deadpool, when the river dwindles so much it essentially grinds to a halt in dammed artificial lakes Powell or Mead.

“Deadpool actually means no more water. It means that the amount of water in the reservoir is so low that no water can pass through the dam to get to the river below the dam. That’s deadpool, and the consequences of that are environmental and economic catastrophe,” Robert Glennon, professor emeritus of water policy and law at the University of Arizona, told Fortune. Last year, federal water managers warned the Colorado River could be faced with deadpool as soon as 2025.

The second option is to cut water supply to the three states by sticking to long-standing priority rights that allot more water to some over others, a legal precedent that has historically benefited California, the state that gets the most water. And the third option is to reduce consumption with equitable cuts to each of the states, which could reduce water supply for each state by as much as 13%. If selected, the third proposal would upend precedent and pave the way for litigation.