OLYMPIA, Wash. — Authorities say outdoor marijuana-growing operations in Washington have continued to decline in 2013.

Eradication teams pulled about 39,000 plants this year across the state, with a little more than 4,000 of those coming from Yakima County, according to the Washington State Patrol.

The statewide count peaked at just more than 609,000 plants in 2009 and came in at 216,000 for last year. Patrol officials attribute the decrease to nearly a decade of focused efforts by multiple law enforcement agencies to chase organized drug traffickers out of the state.

Just more than 214,000 plants were seized in Yakima County in 2008; 96,000 in 2009; 51,000 in 2010; 77,425 in 2011; and 55,352 in 2012. The growing and seizure season typically ends with significant cold weather.

“Our goal has been to keep Washington from becoming a source state for marijuana,” WSP Chief John Batiste said in a news release issued Tuesday. “Everyone has seen the violence that comes with the illegal drug trade, and we will not let that happen here.”

Marijuana growers who use public lands for their operations tend to cause environmental damage and present a threat to legitimate users because they want to protect their plants, officials say. Firearms have been recovered at some of the scenes in Yakima County and other locations.

Lt. Chris Sweet, a spokesman for the patrol’s narcotics section, said there has been some decline in the numbers because officials no longer track operations that involve medical marijuana. But investigators are hearing that the criminal organizations that were using Washington’s public lands for marijuana cultivation now think they should go elsewhere because of the pressure from police.

“It’s definitely a success, and we’re just going to have to wait to see what happens for the next few years,” Sweet said.