An unknown amount of oil leaked from a BP (British Petroleum) refinery in Whiting, Indiana into Lake Michigan after a mechanical problem Monday afternoon, the company confirmed Tuesday.The discharge of oil had stopped, and the leak was contained, BP said in a statement. No injuries were reported, and the effect on Lake Michigan was not immediately clear, as about 60 percent of the lake is covered in ice.BP has deployed booms in the water to keep the spill from spreading and said the oil was in a cove between the refinery’s wastewater treatment plant and a steel mill. Crews were working on the cleanup Tuesday. U.S. federal, state, and Coast Guard officials were at the scene.Winds were pushing the oil onto the shore, while cold temperatures were causing it to harden into a waxy consistency, making it easier to collect, BP spokesman Scott Dean said. He declined to say how much oil spilled.