COEUR d'ALENE — The Idaho Transportation Department confirmed Monday that oil is leaking from construction equipment that fell into Lake Coeur d'Alene more than 30 years ago.

A sheen of oil observed on the water near Higgens Point was first reported on social media late Wednesday. ITD and Department of Environmental Quality officials surveyed the site Thursday morning and containment booms were set along about 75 feet of shoreline.

"We will be adding additional booms to try to keep the oil away from the shoreline and contain it," wrote Megan Jahns, Idaho Transportation Department spokeswoman.

A diver on Friday was unable to see the source of the leak due to darkness. Another dive is expected to occur Wednesday.

Jahns said they hope to get a better look at the existing containment system and repair it if possible.

"We have been consulting with DEQ on how best to respond to the situation," she wrote in an email to The Press.

A sheen of oil drifted along the shoreline and stretched out in a narrow, meandering pattern 50 yards from shore, where the bulldozer is buried in rock and silt in nearly 100 feet of water. It has a protective membrane covering it, Jahns said.

She said ITD does not have an estimate for how much oil has made its way to the surface. She said one cup of product can put a sheen on 20 acres of water.

A D9 dozer fell in the lake during Interstate 90 construction in 1990. It was left there rather than risk tearing up the lake bed and the spawning area, according to a previous Press report.

In 2000 and in 2010, oil leaked to the surface before repairs stopped it.

Wildlife officials have not commented on whether the sheen posed a health threat to the bald eagles that arrive at that part of the lake annually to feed on spawning kokanee.