EUREKA -- State scientists, grappling with an explosion of marijuana growing on the North Coast, recently studied aerial imagery of a small tributary of the Eel River, spawning grounds for endangered coho salmon and other threatened fish.
In the remote, 37-square-mile patch of forest, they counted 281 outdoor pot farms and 286 greenhouses, containing an estimated 20,000 plants, mostly fed by water diverted from creeks or a fork of the Eel. The scientists determined the farms were siphoning roughly 18 million gallons from the watershed every year, largely at the time when the salmon most need it.
"That is just one small watershed," said Scott Bauer, the state scientist in charge of the coho recovery on the North Coast for the Department of Fish and Game. "You extrapolate that for all the other tributaries, just of the Eel, and you get a lot of marijuana sucking up a lot of water. This threatens species we are spending millions of dollars to recover."
The marijuana boom that came with the sudden rise of medical cannabis in California has wreaked havoc on the fragile habitats of the North Coast and other parts of California. With little or no oversight, farmers have illegally mowed down timber, graded mountaintops flat for sprawling greenhouses, dispersed poisons and pesticides, drained streams and polluted watersheds.
Because marijuana is illegal under federal law, most growers still operate in the shadows, and scientists have little hard data on their collective effect. But they are getting ever more ugly snapshots.
A study led by researchers at UC Davis found that a rare forest carnivore called a fisher was being poisoned in Humboldt County and near Yosemite in the Sierra Nevada.
The team concluded in its July report that the weasel-like animals were probably eating rodenticides that marijuana growers employ to keep animals from gnawing on their plants, or they were preying on smaller rodents that had consumed the deadly bait. Forty-six of 58 fisher carcasses the team analyzed had rat poison in their systems.
Mark Higley, a wildlife biologist on the Hoopa Indian Reservation in eastern Humboldt who worked on the study, is incredulous over the poisons that growers are bringing in.
"Carbofuran," he said. "It seems like they're using that to kill bears and things like that that raid their camps. So they mix it up with tuna or sardine, and the bears eat that and die." The insecticide is lethal to humans in small doses, requires a special permit from the EPA and is banned in other countries. Authorities are now regularly finding it at large-scale operations in some of California's most sensitive ecosystems.
It is just one in a litany of pollutants seeping into the watershed from pot farms: fertilizers, soil amendments, miticides, rodenticides, fungicides, plant hormones, diesel fuel, human waste.
Scientists suspect that nutrient runoff from excess potting soil and fertilizers, combined with lower-than-normal river flow due to diversions, has caused a rash of toxic blue-green algae blooms in the North Coast rivers over the past decade.
The cyanobacteria outbreaks threaten public health for swimmers and kill aquatic invertebrates that salmon and steelhead trout eat. Now, officials warn residents in late summer and fall to stay out of certain stretches of water and keep their dogs out. Eleven dogs have died from ingesting the floating algae since 2001.