California is in one of its worst-ever droughts because people are growing too much weed

The rapid expansion of marijuana farms is putting a strain on the state's limited water reserves

A marijuana plant (MARCEL VAN HOORN/AFP/Getty Images)

The current drought in California, one of the most severe on record, could have been exacerbated by marijuana cultivation, scientists say.

Some marijuana farms are sucking more water from the ground than can be replaced, threatening the state’s water entire supply, according to a study published in the Public Library of Science journal.

The amount of water being used to cultivate marijuana was said to be “unsustainable” in the report.

Smaller streams were found to be completely “dewatered” by the demands of marijuana farming, while larger streams experienced substantial “flow diversions and increased temperatures”.

In some areas the water use was so extensive, fish and other aquatic wildlife were threatened.

The study warned: “Continued diversions at a rate necessary to support the current scale of marijuana cultivation in northern California could be catastrophic for aquatic species.”

Marijuana is illegal to use recreationally in California, but the cultivation of marijuana in California has increased rapidly since 1996, when the use and growth of medical marijuana was legalised.

Marijuana is considered particularly water intensive compared to other crops. Wine grapes, for example, require roughly half as much water as marijuana plants.

California consistently outranks all other states for the number of marijuana plants that are eradicated by law enforcement.

The main areas of cultivation are on private property, located in the northwest of the state, primarily because it is “remote, forested, and sparsely populated”.

Therefore, it is often difficult for authorities and scientists to accurately gauge the extent and the impact of the farming.

The state authorities do not regulate marijuana farms and it had been seen as unrealistic to expect that growers would register for permits to divert water.

But that is now changing following concern over the effect on the environment.

The California Water Resources Control Board is developing a permit that growers in 10 northern counties will be required to obtain.

And water diversion permit checks are being stepped up, with fines starting at $8,000 for each transgression.