SAN FRANCISCO (AP) -- Some drought-stricken rivers and streams in Northern California's coastal forests are being polluted and sucked dry by water-guzzling medical marijuana farms, wildlife officials say - an issue that has spurred at least one county to try to outlaw personal grows.

State fish and wildlife officials say much of the marijuana being grown in northern counties under the state's medical pot law is not being used for legal, personal use, but for sale both in California and states where pot is still illegal.

This demand is fueling backyard and larger-scale pot farming, especially in remote Lake, Humboldt and Mendocino counties on the densely forested North Coast, officials said.

"People are coming in, denuding the hillsides, damming the creeks and mixing in fertilizers that are not allowed in the U.S. into our watersheds," said Denise Rushing, a Lake County supervisor who supports an ordinance essentially banning outdoor grows in populated areas.

"When rains come, it flows downstream into the lake and our water supply," she said.

Many affected waterways also contain endangered salmon, steelhead and other creatures protected by state and federal law.

Wildlife biologists noticed streams running dry more often over the 18 years since the state passed Proposition 215, but weren't sure why.

"We knew people were diverting water for marijuana operations, but we wanted to know exactly how much," said Scott Bauer, the department biologist who studied the pot farms' effects on four watersheds. "We didn't know they could consume all the water in a stream."

So Bauer turned to Google mapping technology and satellite data to find out where the many gardens are, and how many plants each contained.

His study estimates that about 30,000 pot plants were being grown in each river system - and he estimates that each plant uses about six gallons per day over marijuana's 150-day growing season. Some growers and others argue the six-gallon estimate is high, and that pot plants can use far less water, depending on size.

He compared that information with government data on stream flows, and visited 32 sites with other biologists to verify the mapping data. He said most grow sites had posted notices identifying them as medical pot farms.

Pot farm pollution has become such a problem in Lake County, south of Bauer's study area, that officials voted unanimously last year to ban outdoor grows.

"Counties are the ultimate arbiter of land use conflict, so while you have a right to grow marijuana for medicinal use, you don't have a right to impinge on someone else's happiness and wellbeing," Rushing said.

Saying they were being demonized, pot users challenged the law, and gathered enough signatures to place a referendum on the June 3 ballot. They argue that grow restrictions like the ones being voted on in Lake County lump the responsible users in with criminals.

"We definitely feel environmental issues are a concern. But more restrictive ... ordinances will force people to start growing in unregulated and illegal places on public land," said Daniel McClean, a registered nurse and medical marijuana user who opposes the outdoor-grow ban.

While some counties are trying to help regulate the environmental effects of pot farms, Bauer hopes his study will lead to better collaboration with growers to help police illegal use of water and pesticides.

Previous collaborative attempts between government and growers have not ended well, said Anthony Silvaggio, a Humboldt State University sociology professor who studies the pot economy.

"The county or state gets in there and starts doing code enforcement on other things," Silvaggio said. "They've done this in the past"

He said pot farmers believe they are being unfairly blamed for killing endangered salmon while decades of timber cutting and overfishing are the real culprits.

However, the environmental damage has led to a split in the marijuana growing community.

One business, the Tea House Collective in Humboldt County, offers medicinal pot to people with prescriptions that it says is farmed by "small scale, environmentally conscious producers."

"Patients who cannot grow their own medicine can rely on our farmers to provide them with the best holistic medicine that is naturally grown, sustainable and forever Humboldt," the group's website advertises.

Despite efforts of some pot farmers to clean things up, the increased water use by farms is a "full-scale environmental disaster," said Fish and Wildlife Lt. John Nores, who leads the agency's Marijuana Enforcement Team.

"Whether it's grown quasi legally under the state's medical marijuana laws, or it's a complete cartel outdoor drug trafficking grow site, there is extreme environmental damage being done at all levels," Nores said.

Officials say until the federal government recognizes California's medical marijuana laws, growers will continue to operate clandestinely to meet market demand for their product due to fear of prosecution. Meantime, enforcing federal and state environmental regulations will be harder.

"If cherry tomatoes were worth $3,000 a pound, and consumption was prohibited in most states, people would be doing the same thing," Nores said.

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Jason Dearen can be reached at http://www.twitter.com/JHDearen

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