North Dakota health officials said drinking water is safe to use following an oil spill in the Montana waters of the Yellowstone River.

The North Dakota Department of Health and the city of Williston in a joint statement said they were still monitoring water levels, though the most recent test data show pollution levels are well below the threat level.

"The tests revealed low levels of hydrocarbon contaminants within the system, but the level of contaminants is decreasing over time, which suggests that the contaminants are now leaving the system," Saturday's statement read.

The Poplar pipeline, operated by Bridger Pipeline, spilled oil into the Yellowstone River in mid January. A unified command responding to the spill said oil recovery continues, with the estimated spill volume reduced from 1,200 to 925 barrels.

Montana's governor declared a brief state of emergency over communities affected by the spill. Residents in and around Glendive, Mont., were ordered to use bottled water, though the all-clear was given last week.

North Dakota officials said they would test the Missouri River system and elsewhere as a precautionary measure.

Unified command in Montana said the pipeline was exposed at the site of the spill, with the river bottom measured at about 1 foot below the oil transit artery. Bridger in 2011 confirmed the pipeline was about 8 feet below the river bed at its shallowest point.

While surveys did not reveal a cause of the Jan. 17 release, unified command said the data will assist investigators in resolving the issue.

River scour was identified as a leading cause in the 2011 oil spill from the Silvertip pipeline, operated by Exxon Mobil. That rupture spilled 1,200 barrels of oil into the Yellowstone River.

Federal regulators last week fined Exxon about $1 million in civil penalties for the spill.

Montana revises oil spill estimates
Glendive, Mont. (UPI) Jan 23, 2015 - With residents clearing their drinking water lines, authorities responding to a Montana oil spill revised the estimated volume of the release to 925 barrels.

The Poplar pipeline, operated by Bridger Pipeline, spilled oil into the Yellowstone River last weekend. A Twitter account set up by a unified command responding to the spill said oil recovery continues, with the estimated volume reduced from 1,200 to 925 barrels.

Recovered an additional 34 barrels of oil from the Poplar Pipeline. Total potential spill reduced to ~925 barrels or ~39k gallons. #glendive— Poplar Response (@poplarresponse) January 23, 2015

The all-clear was given for the region's water treatment plant and residents impacted by the spill were directed to flush their drinking water lines to ensure any contaminants were released. A consumption advisory remains in place as officials warn contaminants may linger in fish for as long as 40 days.

Neither Bridger nor state officials have indicated what caused the release. River scour was in part behind a 2011 release of 1,200 barrels of oil into the Yellowstone River from the Silvertip pipeline, operated by Exxon Mobil.

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