The Los Angeles Times reported Sunday that in one remote, 37-square mile forest patch, scientists found 567 outdoor farms and greenhouses.
Most used water—totaling about 18 million gallons per year—diverted from an Eel River tributary, spawning ground for the endangered coho salmon.
Despite the state push toward decriminalizing marijuana, growers remain rogue and free from oversight.
They have graded mountaintops for greenhouses, illegally cut down trees and in one case poisoned dozens of a rare forest carnivore near Yosemite called a fisher. Scientists determined most had ingested rodenticide used by growers on pot plants.
Researchers are finding a potpourri of contaminants seeping into the watershed from marijuana farms, which are unregulated and largely operate in the shadows. Fungicides, fertilizers, diesel fuel, human waste, plant hormones and soil amendments are some of the others that are ravaging the environment.
Scientists suspect that runoff from potting soil and fertilizers, combined with lower-than-normal river flow due to water diversions, has resulted in a spate of toxic algae blooms in North Coast rivers over the past decade.
The cyanobacteria outbreaks threaten public health for swimmers and kill food that salmon and steelhead trout eat. Eleven dogs have died since 2001 after ingesting the blooms.
Growers are required to obtain permits to take water from a creek but Tony LaBanca, senior environmental scientist with the state Department of Fish and Game, told the Times that less than 1 percent of growers comply with the permits, usually only after an enforcement action.
Other research has shown other effects of the state's marijuana crops—electricity use. A study in the journal Energy Policy estimated that indoor marijuana cultivation could be consuming nine percent of the state's household electric power use.
Information from: Los Angeles Times, http://www.latimes.com