This story was originally published by KUNC .

The Colorado River basin has lost huge volumes of groundwater over the past two decades according to a new report from researchers at Arizona State University. Researchers used data from NASA satellites to map the rapidly depleting resource.

The region, which includes seven western states , has lost 27.8 million acre-feet of groundwater since 2003. That’s roughly the volume of Lake Mead, the nation’s largest reservoir.

The findings add a layer of complication for the already-stressed Colorado River. As demand for its water outpaces supply, more users may be turning to groundwater instead, which is often less regulated than water from aboveground rivers and streams.

The majority of water conservation work throughout the Colorado Rive

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