In 1922, seven Western states — Colorado, Utah, New Mexico, Arizona, Nevada, Wyoming and California — drew up an agreement on how to divide the waters of the Colorado River. But there was one big problem with the plan: They overestimated how much water the river could provide.

As a result, each state was promised more water than actually exists. This miscalculation — and the subsequent mismanagement of water resources in those states — has created a water crisis that now affects nearly 40 million Americans.

Environmental reporter Abrahm Lustgarten began investigating the water crisis a year and a half ago for the ProPublica series Killing the Colorado. He tells Fresh Air's Dave Davies that he initially thought the water crisis was the result of climate change or drought. Instead, Lustgarten says, "It's the policy and the management that seem to be having a greater effect than the climate."

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Interview Highlights

On how, in the 1920s, seven Western states decided how they would divide up the waters of the Colorado River

The states came together and negotiated, actually, at the behest of Herbert Hoover, for how they would divide up that river. To do that, they calculated what they thought was the total flow of the river, thought they'd leave a little bit in the river for the health of the ecosystem, and divided up what they thought remained. It has turned out over the years that far less than that flows in the river. ... What that means is from the very start the Colorado River has been over-allocated — not all of those states yet take the maximum amount they're allowed to, but if they did, each of those states have been promised collectively more water than actually exists, and that's the very premise of water use in the West. Before drought, before climate change, before expansion and population, they began with the premise of thinking they had more water than they actually had.