Illegal cartels use public forests to grow their marijuana crops, contaminating nearby wildlife and water sources.

The large amounts of insecticides and chemicals used to breed black market marijuana plants have been affecting the health of wildlife and water sources in several public forests across the U.S.. The damage to these crops could last decades.

NPR spoke with several experts and employees from the U.S. Forest Service, who said that it’s very common for drug cartels to target dense forests to hide their grow operations in plain sight. These illegal marijuana sites can go undetected for years.

“The true crime here is the fact that they’re killing off basically America’s public lands, killing off the wildlife, killing off our water. This is stuff that, you know, it’s not gonna repair itself,” explains Kevin Meyer, law enforcement assistant from the U.S. Forest Service.

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The chemicals and pesticides used on these sites, many of which are banned in the U.S., are incredibly damaging to forest ecosystems. “A quarter teaspoon could kill a 600-pound black bear. So obviously just a tiny amount can kill a human. It remains in an ecosystem for a long period of time,” says wildlife ecologist Greta Wengert, regarding the insecticide carbofuran.

While this problem has existed for as long as marijuana has been sold, it’s only recently that cartel growers have started using more chemicals and pesticide products, spreading them throughout large plots of land without regard for their surroundings.

Aside from hurting the plants and the animals that surround the area, chemicals like these stay in the ecosystem for years, reducing animal populations and influencing future generations of animals. These substances infect mothers and their offspring, causing deaths that will later infect insects and animals that feed on the remains. It’s a vicious cycle that perpetuates and affects all wildlife far beyond the one spot where the marijuana was cultivated.

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While the state of California has set up several organizations designed to prevent the spread of these sites, experts estimate that they’re only able to capture around half of them each year. Aside from the tremendous ecological damage, these sites are also affecting marijuana’s legal market, undercutting it by around 50%.

“A lot of the product that they’re growing is filled with these poisons and it’s likely finding its way into the market in various forms — flower, oils and vape pens,” explains Rich McIntyre, director of the Cannabis Removal on Public Lands Project.