The legalization of cannabis in California has done almost nothing to halt illegal marijuana growing by Mexican drug cartels, which are laying bare large swaths of national forest in California, poisoning wildlife, and siphoning precious water out of creeks and rivers, U.S. Attorney McGregor Scott said Tuesday.

The situation is so dire that federal, state and local law enforcement officials are using $2.5 million from the Trump administration this year to crack down on illegal growers, who Scott said have been brazenly setting booby traps, confronting hikers and attacking federal drug-sniffing dogs with knives.

Instead of fading away after legal marijuana retail sales went into effect this year, the problem has gotten worse, according to Scott, who was joined in a news conference Tuesday in Sacramento by California Attorney General Xavier Becerra and other federal forestry and law enforcement officials.

Most alarming, Scott said, is the increasing use of carbofuran, a federally restricted insecticide so powerful that a teaspoon of it can kill a 600-pound African lion. The insecticide is banned in California.

The problem of illegal growing operations and contaminated lands “is biblical in proportion,” he said. “The chemicals have gone to a different level.”

The cartels, mainly from Mexico, use 760 tons of fertilizer on 400 grows every year hidden on the 20 million acres of national forest land in California, officials said.

The growers clear-cut trees, remove native vegetation, cause erosion, shoot deer and other animals, and litter the landscape with garbage and human waste. They also divert hundreds of millions of gallons of water from streams and creeks, and the runoff is generally contaminated with pesticides, which are also found in the plants, soil and wildlife in the area.

This year, 70 percent of the endangered spotted owls tested near sites that had been used for illegal marijuana cultivation were found to have one rodenticide or more in their systems, officials said. One owl died, leaving a clutch of eggs. Last year, 43 poisoned animals were found, including deer, bears, foxes, coyotes, rabbits and rare Pacific fishers. Another 47 animals had been shot, most likely by illegal growers, authorities said.

Since 2012, 17 Pacific fishers have been killed by pesticides at grow sites, said Mourad Gabriel, the director of the Integral Ecology Research Center, a wildlife and environmental research nonprofit. He said carbofuran was found in 78 percent of the plantations eradicated in 2017. That’s compared with 40 percent in 2015 and only 10 to 12 percent in 2012, when he conducted the first scientific study of illegal marijuana grow sites.

“It’s concerning, because now when we go into these sites we find contamination in the native vegetation, the soil, the water; and it’s increasing,” said Gabriel, whose research is funded by state and federal grants. “Those sites are still contaminated two or three years later.”

In all, 1.4 million illegally grown marijuana plants were destroyed in raids in national forests in California in 2017.

Bill Ruzzamenti, the former director of the Campaign Against Marijuana Planting, said California supplies 60 to 80 percent of all the marijuana consumed in the nation. In 2016, he said, 11 million pounds left the state, which is illegal under Proposition 64, the initiative that legalized the drug for recreational use in the state.

The people guarding the grow sites are inevitably armed and “a public safety risk to all of us,” said Becerra.

Margaret Mims, the sheriff of Fresno County, said hikers, backpackers and nature lovers have reported running across fishhooks hanging at eye level and trip wires possibly attached to shotguns.

“I have grandkids and I like to go fishing, but there are places we will not go because I am afraid for my grandkids,” said Ruzzamenti, who is now director of the federal High Intensity Drug Trafficking Areas program. “That should be unacceptable to everybody.”

The problem isn’t new. Bootleg cannabis has been circulating around Mendocino, Humboldt and Trinity counties — the famed Emerald Triangle — for decades, and backwoods growing is ingrained in the culture.

Ruzzamenti said he has been trying to eradicate black-market growing on public lands since 1983. And Mexican cartels aren’t the only problem. Only a few hundred of the estimated 12,500 retail operators in the state last year have become licensed so far, according to industry officials.

In Mendocino County alone, as many as 75 percent of residents in some remote areas are marijuana growers, and only about 10 percent of the crop is being grown legally.

The issue has taken on a new level of importance as the multibillion-dollar California cannabis industry begins to ramp up. Legal growers and retailers want desperately to protect the regulated, taxed marijuana market in California.

The hope is that taxes collected by the government can fund law enforcement efforts, which will, in turn, deter illegal operations and generate additional taxes. Wholesale prices for marijuana are also expected to drop with the mainstreaming of the industry, providing less incentive for bad actors.

But so far that hasn’t worked. In all, California collected $60.9 million in excise, cultivation and sales taxes related to legal marijuana for the first three months of 2018. Gov. Jerry Brown’s January budget proposal predicted that $175 million would pour in over the first six months from the new taxes. That would have translated to $87.5 million in January, February and March.

In his updated budget plan released earlier this month, Brown proposed spending $14 million to create four investigative teams and one interdiction team to combat illegal activities, tax evasion and crime. The money would come from tax revenue and licensing fees over two years.

Even though marijuana is still illegal on the federal level, Scott said the U.S. Attorney’s office plans to focus only on illegal growers on public lands.

Becerra said that without the help of the federal government, California wouldn’t be able to handle the problem.

“You gotta make it so crime doesn’t pay,” he said.

Peter Fimrite is a San Francisco Chronicle staff writer. Email: pfimrite@sfchronicle.com. Twitter: @pfimrite