KENNEWICK — As much as 300 gallons of oil may have leaked into the Snake River from a power-generating turbine at Lower Monumental Dam.

The Army Corps of Engineers reported the suspected spill this week, but it’s unclear when it happened.

The Army Corps disclosed the incident to regulators and the environmental group Columbia Riverkeeper under the terms of a 2014 settlement agreement.

Columbia Riverkeeper had sued to stop oil releases from the eight dams on the lower Snake and Columbia rivers.

The group issued a statement calling the most recent disclosure the latest in a series of spills that highlight the threat posed by the four aging Snake River dams.

The Corps reported that 200 to 300 gallons of unspecified “turbine oil” may have leaked from a turbine shaft at Lower Monumental, about 40 miles northeast of the Tri-Cities.

The Washington Department of Ecology confirmed it was also notified of the potential spill, which will be confirmed once the Army Corps takes an inventory of oil in the turbine.

A state spokesman said the agency has received no reports of a sheen appearing on the river.

Columbia Riverkeeper issued a statement about its continuing concerns about the dams.

“Oil pollution from Lower Monumental Dam is just one more reason to remove the four obsolete, aging dams on the lower Snake River,” Miles Johnson, senior attorney for the group, said in a news release.

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