AHSAHKA, Idaho — Cleanup operations are continuing Tuesday in northern Idaho following an oil spill into the North Fork of the Clearwater River from a hydroelectric turbine undergoing rehabilitation work at Dworshak Dam.

A U.S. Army Corps of Engineers spokeswoman says a sheen of the light-grade turbine oil was spotted after the Monday morning spill downstream where the North Fork enters the main Clearwater River but the sheen dissipated.

The agency in a statement Tuesday says the exact quantity of oil spilled is still being determined but gave an initial estimate of 10 to 20 gallons.

The agency says reservoir managers reduced flows and also notified Dworshak National Fish Hatchery at the confluence of the North Fork and Clearwater rivers.

The U.S. Fish and Wildlife Service says there’s been no impact at the hatchery but absorbent booms have been placed near the water intake.