BILLINGS (AP) — Cleanup work on a 30,000-gallon oil pipeline spill into the Yellowstone River near Glendive is effectively on hold for a month or more until ice on the river melts, state and pipeline company officials said Tuesday.

About 25 people remain at the site to watch for oil-damaged wildlife and respond to any crude oil seen on the river. That’s down from a peak of about 125 people during the initial response, officials said.

Less than 10 percent of the oil that spilled into the river has been recovered. It’s uncertain if that figure will significantly increase because much of the crude likely has dispersed as it was carried down the river, according to state officials.

“Right now we’re in this phase where we’re watching it, but we’ll see what happens when the ice breaks up,” said Jeni Garcin with the Montana Department of Environmental Quality.

The monitoring area spans a 90-mile stretch of the Yellowstone, from the spill site downstream to a bridge just across the North Dakota border.

The cause of the Jan. 17 accident along Bridger Pipeline LLC’s Poplar line remains under investigation.

The spill temporarily fouled Glendive’s drinking water supply and renewed calls for increased government oversight of the nation’s aging pipeline network. It was the second significant oil pipeline spill into the Yellowstone in less than four years, following a 2011 spill near Laurel.

The section of line that broke upstream of Glendive was installed in 1967. It was originally buried beneath the river but somehow became exposed in the last several years, according to Bridger Pipeline. 

Officials are investigating whether an ice jam on the river near the spill last year could have played a role. A large enough ice jam can scour a river bottom, experts say, potentially scraping away the cover over a pipeline.

How long this year’s ice holds back the remaining cleanup work depends on weather conditions over the coming weeks. Officials handling the spill said they expect their work to resume in early- to mid-March. Local residents say ice can linger on the Yellowstone into April.

During a warm spell last week, government officials and a Bridger Pipeline spokesman were hobbled by another problem: The ice on the river was becoming too brittle to work on safely.

“We started the week thinking the ice would get too soft. We ended the week with it getting too hard. In both cases, we ended up being in a place where there’s no recoverable oil to get,” Bridger Pipeline spokesman Bill Salvin said Tuesday.