© 2017 The Community Governance Partnership

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 “Trespass grows” are illicit cannabis grows on public lands. Trespass grows constitute one of California’s leading environmental threats by poisoning wildlife on a landscape scale, contaminating water and soil with EPA-banned toxicants , and severely de-watering watersheds.

The Basics

  • Trespass grows account for 40-70% of CA’s illicit cannabis market [1]

  • 80% of trespass grows are on national forest (NF) lands [2]

  • Over 90% of trespass grows are controlled by drug trafficking organizations (DTOs) [3]

  • Since 2000, over 23 million plants have been eradicated on CA NFs [4]

  • Since 2016, over 3 million plants have been eradicated on CA NFs [4]

  • Only 1 in 5 public lands cannabis plants are eradicated annually [2]

  • In 2018, 90% of sites contained lethal, controlled or banned pesticides [3], including Sarin-based malathion, Brodifacoum/Bromadiolone, Carbofuran, Methamidophos, and Cholecalciferol [5]

  • 30-40% of trespass grows go undetected [13]

Impacts to Wildlife


  • 70% of Northern Spotted Owls (ESA Listed) poisoned by rodenticide [6]

  • 80% of Pacific fishers (ESA Candidate) tested positive for up to 5 rodenticides [7]

  • 92% of mountain lions statewide test positive for one or more pesticide, particularly rodenticides [8]

Impacts to Water

  • More than 9 billion gallons of water per year are illegally diverted for trespass grows, or 27,600 acre feet (a yearly water supply for nearly 30,000 homes, or the City of Redding) [12]

  • Watershed diversion from trespass grows can account for 23-50% of total surface flow [9]

  • Approximately 6 gallons of water per plant per day [10]

  • Water theft exceeds minimum instream flows for certain watersheds [11]

Impacts to Communities

  • Contaminated watersheds; communities/tribes at great risk of toxicant exposure

  • Reduced flows for fisheries, agriculture, tribal gathering, timber production, etc.

  • Negative impact to local and state economy (e.g. costly clean-ups, increased enforcement)

  • Reduced access to public lands as “no-go areas” due to DTO grows

  • Recreation, hunting and other uses of public lands poses toxicant exposure risk

  • Undercuts the legal cannabis market

  • Loss in ecosystem services, such as clean water and air



[1] Estimates from ONDCP, HITDA, Don Hoang (Forest Service Special Agent in Charge of the Pacific SW Region), Dr. Mourad Gabriel (Co-Director at the Integral Ecology Research Center), Tommy Lannier (Director of the National Marijuana Initiative)


[2] Ferrell, David L. 2016. Issue: Marijuana Cultivation on National Forest System and other public lands, environmental effects, and cooperative activities. US Forest Service Report to Congress. Washington, D.C., USA.


[3] Law enforcement statistics based on eradications

[4] Hoang, Don. 2019. Illegal Marijuana Production and Environmental Impact to National Forest System Lands. US Forest Service Publication 5300, Washington, D.C., USA.


[5] Integral Ecology Research Center trespass grow test results and first-hand reclamations


[6] Gabriel, M. W., L. V. Diller, J. P. Dumbacher, G. M. Wengert, J. M. Higley, R. H. Poppenga, and S. Mendia. 2018. Exposure to rodenticides in Northern Spotted and Barred Owls on remote forest lands in northwestern California: evidence of food web contamination. Avian Conservation and Ecology 13(1):2.

[7] M.W. Gabriel, L.W. Woods, R. Poppenga, R.A. Sweitzer, C. Thompson, S.M. Matthews, J.M. Higley, S.M. Keller, K. Purcell, R.H. Barrett, G.M. Wengert, B.N. Sacks, D.L. Clifford, (2012). Anticoagulant rodenticides on our public and community lands: Spatial distribution of exposure and poisoning of a rare forest carnivore. PLoS ONE. 2012 Jul 13; 7(7):e40163.               

[8] California Department of Pesticide Regulation. 2018. An Investigation of anticoagulant rodenticide data submitted to the Department of Pesticide Regulation. California Department of Pesticide Regulation, Sacramento, CA, USA.


[9] Bauer, S., J. Olson, A. Cockrill, M. van Hattem, L. Miller, M. Tauzer, G. Leppig. 2015. Impacts of Surface Water Diversions for Marijuana Cultivation on Aquatic Habitat in Four Northwestern California Watersheds. PLOS ONE 10(9): e0137935.


[10] Hendron, J. 2017. Illegal Marijuana Sites: A stain on Public Lands. US Fish & Wildlife Service newsroom. <https://www.fws.gov/cno/newsroom/featured/2017/illegal_marijuana_sites>. Accessed 24 May 2019.


[11] California Council of Land Trusts. 2017. Environmental Impacts of Illegal Marijuana Cultivation. Conservation Frontiers (6.1):1-4.


[12] Basic calculation based on law enforcement estimates of number of plants removed, and water requirements per plant per growing season


[13] Estimates from IERC trespass grow GIS modelling and analysis


For more information, please visit www.cropproject.org