A study published last week posits a parched forecast for several North Coast watersheds that host concentrated marijuana cultivation sites.

The report, co-written by scientists from the California Department of Fish and Wildlife and the National Marine Fisheries Service, outlines the stream-sucking impacts of grows in the areas of Upper Redwood Creek, Salmon Creek and Redwood Creek South, located in Humboldt County, and Mendocino County's Outlet Creek.

Using satellite imagery, stream flow data and anecdotal evidence gathered by tagging along during raids, the team determined that in three out of the four watersheds, "water demands for marijuana cultivation exceed streamflow during low-flow periods."

In other words, the researchers predict that during summertime — when growing marijuana plants require the most water and rainfall all but ceases — many stream beds will dry up.

This won't come as much of a surprise to anyone who's seen maps like the ones environmental biologist Scott Bauer (who co-authored the study for Fish and Wildlife) has produced, showing clusters of grows on tributaries of many North Coast rivers.

And while research areas contain tens of thousands of marijuana plants, "the total number of registered, active diversions on file with the State Water Resources Control Board accounted less than half of the number of parcels with [grows] that were visible from aerial imagery," the study reads. "In some watersheds, the number was as low as 6 percent."

The research indicates that relatively small, private-land grows have proliferated in the last two decades. Most of those rely on surface water to irrigate crops, meaning big draws on streams from many users. That adds up, the research shows, and it can have devastating effects.

"Flow modification is one of the greatest threats to aquatic biodiversity," the report reads. But before now, most research on the impacts of dewatering watersheds has been limited to large-scale projects like hydroelectric dams.

The focus areas of the Fish and Wildlife study are rich in fragile species, including the coho and Chinook salmon and steelhead trout, each of which are considered threatened by the federal and/or state government.

Even for the larger streams that aren't anticipated to run completely dry, lower flows are correlated with rising temperatures, which hinder salmon's ability to reproduce and survive. "Given the specter of climate change-induced ... droughts and diminished summer stream flows in the region, continued diversions at a rate necessary to support the current scale of marijuana cultivation in Northern California could be catastrophic for aquatic species," the report reads.

Fish, amphibians and other water-reliant wildlife aren't the researchers' only concern either. "On a localized scale, with regional implications, this study detects an emerging threat to not only aquatic biodiversity but also human water security, since surface water supplies most of the water for domestic uses in watersheds throughout Northwestern California."

One can imagine a farmer, surprised by a usually reliant stream's mid-season shrinkage, taking matters into his or her own hands and stalking up a creek bed with bolt cutters, lopping every upstream water pipe along the way.

Bauer and his co-authors call for more research of streamflow impacts, more enforcement of illegal diversions, more education of best practices for growers, and careful attention to land use policies for local and state legislators.

(Read the full 25-page report here.)

After all, pot is for smoking; water's for fighting.

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