When the Colorado River Compact was negotiated in 1922 to divide the river’s flow among the seven western U.S. states that span its basin, the representatives of the upper basin states were driven by the realization that they weren’t using much water at the time, but some day they would want to.

Flaming Gorge Reservoir, Green River, courtesy USBR

Under western U.S. water law’s doctrine of prior appropriation, people who show up late to the party get less, but the compact’s negotiators locked in a share for the upper basin states for future use. That underlying principal is now on display in Wyoming, where worries are growing that a share of the water still unused might be lost. The AP’s Ben Neary had an excellent piece earlier this month exploring the dilemma:

Wyoming has an unusual problem among the states in the Colorado River system: lots of water and, other than supporting some fine trout fishing, no way to put a significant amount of it to use.

Yet increasing demand for water in the upper Colorado River basin, combined with new government predictions that climate change could reduce future water supplies, are ratcheting up concerns in Wyoming about how to preserve the state’s share for the day when it’s needed.

The fear in Wyoming involves its neighbors to the south, in Colorado, who are talking about major water project development that would move water from the Colorado Basin across the Continental Divide to the east slope, where Colorado’s biggest cities are located.

Wyoming’s surplus water situation has worried state lawmakers for years.

“At some point are they simply going to say, ‘You didn’t use it, and when you didn’t use it, you lost it,'” said Republican Rep. Kermit Brown of Laramie.

This may explain the rush to squeeze the last bits of water out of the unused Upper Basin share of the Colorado, a point that Jennifer Pitt of the Environmental Defense Fund made in Congressional testimony last month:

[T]here appears to be a race among the states to develop the next big use of water, because for water users who don’t get their straw into the system first, their risk of curtailment increases. This ‘race to develop’ increases risk for many water users in the basin. It would be better to slow down on new developments and first work out interstate agreements on what happens in the event of a call on the Compact.