SAN FRANCISCO -- 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 still is 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.
So Mr. 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.