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Thirsty marijuana plants cause concern in California

Marijuana farmers in northern California rig up their own systems to irrigate their plants. The Nature Conservancy

Golf courses, manicured lawns, and almond trees are getting all the bad press recently for sucking up California’s scarce water supplies, but there’s another hog at the trough — marijuana.

More than 60 percent of all marijuana consumed in the United States is grown in the Golden State, and researchers have found that a boom in production over the last 20 years is depleting streams and endangering already vulnerable animal populations. Those conclusions appear in a paper published earlier this month in Bioscience, by a team of ecologists from the University of California, Berkeley and The Nature Conservancy. The study was prompted when researchers found that the abundance of pot farms in northern California was disrupting other research projects.

“You can’t spend time walking around remote watersheds without encountering illegal marijuana growth,” says Sally Thompson, an ecohydrologist at Berkeley and coauthor the study. “We’d send a student to map a small [area] and they’d have to turn around because they’d encounter an illegal marijuana garden.”


This got Thompson and her colleagues thinking about how these illegal farms were affecting California’s environment. Most of the farms are small — an acre or less — and they tend to cluster in the far northern part of the state, a mountainous and mostly uninhabited region whose remoteness offers obvious advantages if you want to engage in illegal activity. One of those advantages is not, however, ready access to irrigation, which forces marijuana farmers — who range from mom and pop growers to large syndicates — to rig up their own systems.

“These plantations are being watered by pipes dumped right into streams,” she says.

Marijuana is a water-intensive crop. Each plant consumes about 22 liters of water a day and a square kilometer of plants can consume 430 million gallons in a growing season, which runs from June to October. This is twice the water consumed by a comparable amount of wine grapes.

Because these farms are located up in the mountains, they tap into streams before they’ve had a chance to build up volume, and can cause them to run completely dry. “If you take 40 acres of this thirsty plant and put it in a remote part of the landscape, where streams are small and just starting to begin, it’s enough to dewater the stream,” Thompson says.


Legalization, she argues, could draw marijuana growers out of the hinterlands, into more central regions where water supplies aren’t as vulnerable and water consumption can be monitored. And, while the legalization of marijuana in Colorado and Washington would seem to suggest that policy is moving in this direction, Thompson notes that the legal status of marijuana cultivation hasn’t changed much: It’s still illegal to grow it in Washington, and cultivation exists in a kind of legal gray area in Colorado.

In California, marijuana use remains illegal following a failed legalization referendum in 2010. Today, however, polls indicate that attitudes are changing, and with the state staring down a water crisis that calls its very existence into question, water could be the factor that pushes legalization over the finish line.

Kevin Hartnett is a writer in South Carolina. He can be reached at


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