Studying aerial photographs of four watersheds within Northern California's so-called Emerald Triangle, Bauer found that the area under marijuana cultivation doubled between 2009 and 2012. It continues to grow, with increasing environmental consequences.
Bauer presented data to CNBC indicating that growers are drawing more than 156,000 gallons of water from a single tributary of the Eel River, in Mendocino County, every day.
The average marijuana plant needs about 6 gallons of water a day, depending on its size and whether it's grown inside or outside, according to a local report that cited research. Pot growers object to that number, saying that the actual water use of a pot plant is much less.
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Although the marijuana business has helped revive the local economy, residents may now be feeling the effects of living alongside growers. And, as growers—some legal, some not—face an ongoing, severe drought, local law enforcement officers expect the fight over natural resources to intensify.
"I never want to see crime increase, but I have a feeling it will, because of the commodities that are up here," said Humboldt County Sheriff Mike Downey. "When we get to the end of the grow season, which is August and September, the need for enhanced water availability is gonna be there, and I don't think the water's going to be there, so you're going to see people, I believe, having some conflict over water rights."
Stream water rules in California are the same for growers of marijuana as they are for growers of any crop: Growers should divert no more than 10 percent of a stream's flow, and they should halt diversion altogether during late summer, when fish are most vulnerable to low water levels. But Bauer pointed out that those rules apply to permit holders, and most marijuana growers haven't bothered to get permits.
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With so much of California's cannabis business operating in the more lucrative underground market, and with so many growers across the region (see the map below), the California Department of Fish and Wildlife and the Humboldt County Sheriff's office say they lack the resources to eradicate all offenders. So they target the most egregious.