NILES, Ohio - It all started just after 1 p.m. Friday, when a cyclist on the bike trail in Niles noticed a sizable oil sheen on the Mahoning River.

By that time, the oil sheen spread from one side of the bank to the other.

Five different fire departments responded and searched up the river for the source of the sheen and found it at Arcelor Mittal Steel on South Main Street in Warren Township.

They produce coke which is a coal-like substance used in the steel making process.

"Pretty sure at this point we have the source stopped but now what we are trying to do is catch as much oil as we can or product. I'm not sure what the product is at this point," says Weathersfield Fire Chief Randall Pugh.

EPA officials say Mittal Steel is cooperating with clean up efforts. They deployed vacuum trucks to the source of the spill area to collect the petroleum product from a ditch that flows out of the steel plant into a small reservoir and then into the river.

Investigators say a faulty oil-water separator overflowed and caused the spill.

Crews have set up booms along various points on the Mahoning River. The boom is collecting a lot of the petroleum product that's going down the river and there's a lot of it that needs to be siphoned up later.

"Stop the product at two different locations here at West Park and there's an operation on Belmont Avenue. At this point, put another boom in with absorbents and try to catch as much as we can there," says Pugh.

It's hoped they can stop the bulk of the petroleum product from flowing into lower Mahoning County.

None of the water is used for consumption but it's unknown what kind of effect the spill will have on the local environment.

The Mahoning eventually flows into the Ohio river.

The Ohio EPA and Emergency Management crews from Trumbull and Mahoning counties are expected to continue the clean-up efforts for the next several days.