TOPEKA, Kan. — An oil spill in a creek in northeastern Kansas this week is the largest for an onshore crude pipeline in more than nine years and by far the biggest in the history of the Keystone pipeline, according to federal data.

Canada-based TC Energy on Thursday estimated the spill at about 14,000 barrels, or 588,000 gallons. It said the affected pipeline segment had been “isolated” and the oil contained at the site with booms, or barriers. TC Energy, however, did not say how the spill occurred.

After a drop in pressure on the pipeline that carries oil from Canada to the Texas Gulf Coast, the company said it shut down its Keystone system Wednesday night. Oil spilled into a creek in Washington County, Kansas, about 150 miles northwest of Kansas City.

Zack Pistora, a lobbyist for the Sierra Club in Kansas, noted the spill in his state was larger than all of the 22 previous spills combined on the Keystone pipeline, which began operations in 2010.

“This is going to be months, maybe even years before we get the full handle on this disaster and know the extent of the damage and get it all cleaned up,” he said.

In September 2013, a Tesoro Corp. pipeline in North Dakota ruptured and spilled 20,600 barrels, according to U.S. Department of Transportation data. The company, which worked to recover oil for years but only recovered a fraction of the spill, said a lightning strike may have caused that break.

A more expensive spill happened in July 2010, when an Enbridge Inc. pipeline in Michigan ruptured and spilled more than 20,000 barrels into Talmadge Creek and the Kalamazoo River. Hundreds of homes and businesses were evacuated and federal regulators later ordered Enbridge to dredge the contaminated sediment from the river.

The Keystone pipeline’s previous largest spill came in 2017, when more than 6,500 barrels were spilled near Amherst, South Dakota, according to a U.S. Government Accountability Office report released last year. The second largest, 4,515 barrels, occurred in 2019 near Edinburg, North Dakota.

The U.S. Environmental Protection Agency said drinking water wells were not affected by this week’s spill and the oil didn’t move from the creek to larger waterways. The spill was in pastureland about 5 miles northeast of Washington, the county seat of about 1,100 residents, and no evacuations were ordered.

TC Energy said it had set up environmental monitoring at the site, including around-the-clock air quality monitoring.

Concerns that spills could pollute waterways spurred opposition to plans by TC Energy to build another crude oil pipeline in the Keystone system, the 1,200-mile Keystone XL, which would have cut across Montana, South Dakota and Nebraska. Critics also argued that using crude from western Canada’s oil sands would worsen climate change, and President Joe Biden’s cancellation of a U.S. permit for the project led the company to pull the plug last year.