Illegal cannabis grows on California public lands continue to leave behind trash, pesticides and fertilizers that environmental researchers say can contaminate ecosystems and watersheds long after law enforcement eradicates the plants, according to reporting by the Associated Press in partnership with CalMatters.
In Shasta-Trinity National Forest, ecologist Greta Wengert described visiting sites where enforcement had moved through months earlier but hazardous materials still sat in place. At one hillside grow, she looked at pesticide sprayers that animals had gnawed open, releasing chemicals into the environment, she said—an example of the kind of ongoing exposure she and colleagues have warned about for years.
Wengert, who co-founded the Integral Ecology Research Center, has tracked the post-raid cleanup problem by compiling site counts from what her team has documented on public land. She has tallied nearly 7,000 abandoned sites like the one investigators visited, and she said only 587 have been at least partly cleaned up. She said no government agency can provide a comprehensive total and that several agencies routed CalMatters to her nonprofit for an unofficial tally.
Wengert and other researchers also warn that the impacts can outlast the raids themselves. Co-director Mourad Gabriel, who previously spearheaded a U.S. Forest Service effort tackling trespass grows on public lands, told researchers they cannot “push it” until they have the data, describing how the contamination can persist across the landscape. Wengert and Gabriel have reported detecting dangerous pesticides in nearby creeks more than a year after raids, and they have also documented cases of poisoned wildlife.
In recent work described in the reporting, researchers published with scientists at the U.S. Geological Survey found that illegal grows “pulsed” pollutants from a range of materials—plastic, painkillers, personal care products, pot and pesticides—into soil that could be detected months or even years later, with some contaminants also appearing in nearby streams. The same research described concentrations diminishing over time as chemicals disperse and wash into waterways, but it also emphasized that remote habitats and headwaters are still not where the chemicals should be.
For California’s public lands, researchers say cleanup capacity and funding gaps help explain why hazards can remain. The reporting cites U.S. Forest Service statements to CalMatters that a cleanup backlog for national forests is driven by limited funding and a shortage of personnel trained to identify and remove hazardous materials. In the same account, a Forest Service spokesperson said the federal government had dedicated no funding to the Forest Service to clean up the hazardous remnants at such sites.
The broader enforcement-and-cleanup split sits at the center of the dispute over who addresses the lingering damage. Federal land managers and California officials say the federal government owns nearly half of California’s more than 100 million acres, but they described the cleanup responsibilities as falling largely to a patchwork of agencies and lawmakers across state and federal land. California Department of Fish and Wildlife officials said the state’s policy is to clean up grows spotted on its wildlife areas, ecological reserves and other properties, while staff said they assist on federal land “when asked” but that it is not their mandate.
California’s system is partly funded through its legalized cannabis market. The reporting says fees and taxes support the Fish and Wildlife cannabis program and grants for rehabilitating places damaged by cultivation, including potential cleanup work. The department told CalMatters it has removed almost 350,000 pounds of trash and more than 920 pesticide containers from grows on public lands over nearly a decade, but the reporting describes lawmakers and researchers saying that total progress remains too slow relative to the scale of the abandoned sites.
Former Assemblymember Jim Wood, a North Coast Democrat, said cleanup efforts have not matched the urgency of the damage to watersheds and the people who depend on them. He said in 2024, as he prepared to leave office, that the work still “doesn’t reflect what I see is the urgency to watersheds, and the water and the people that are served by them.” In 2024, lawmakers passed Wood’s bill directing the Fish and Wildlife department to conduct a study informing a statewide cleanup strategy for cannabis grows, and requiring regular reports to the legislature on illegal cultivation and restoration efforts across public and private lands.
While the study was described as not due until next year, the reporting also points to a need for practical “playbooks” for cleanup and hazardous-waste handling as new grows emerge across the landscape. Cannabis program director Amelia Wright said the state’s restoration effort is still creating its approach, describing it as “such redemption right now for many of us” and saying, “So we didn’t have a playbook — we’re still creating it.”
The reporting also describes federal lawmakers’ pressure for more resources and staff. U.S. Rep. Jared Huffman said he has tried repeatedly to direct more funding to cleaning up trespass grows on federal lands but with “little success in Congress,” adding that “It’s clearly not enough.” The account also cites staffing changes described by a Forest Service spokesperson under the Trump administration, saying about 5,000 non-fire employees “have either offboarded or are in the process of doing so” through voluntary separation programs, and Huffman characterized the effect as the agency being “gutted.”
At one grow site described in the reporting, researchers documented contaminants as part of a U.S. Forest Service-funded investigation into wildlife around cultivation sites. Later, the California Department of Fish and Wildlife carried out a helicopter-assisted cleanup, removing nearly 1,500 pounds of trash, 4,000 feet of irrigation pipe and seven pesticide containers. Afterward, Gabriel’s team reported finding residue in pesticide sprayers from a chemical class that includes carbofuran, which he said is dangerous and illegal, and he warned that there is a “proper way” and “there is a cowboy way” to clean up.
For researchers and officials, that gap between eradication and safe remediation is what turns abandoned grow sites into continuing environmental hazards. With thousands of sites described as remaining across California, Wengert and others framed the cleanup backlog not as a temporary problem but as long-term contamination risks that can threaten forests, waterways and wildlife for years.