On Thursday, BP more than doubled is initial estimates of the amount of crude oil spilled into Lake Michigan earlier this week.

BP workers at the company's Whiting refinery in northwest Indiana on Monday reported the oil leak into the lake, which is the source of drinking water for 7 million people in Chicago and its suburbs, according to the Los Angeles Times.

The petroleum company, also responsible for the massive oil spill in the Gulf of Mexico back in 2010, initially estimated it had spilled between nine to 18 barrels into the lake, however, its most recent estimate released Thursday put it at 15 to 39 barrels.

One barrel of crude oil is the equivalent of 42 gallons.

The U.S. Coast Guard and the Environmental Protection Agency have been involved with the cleanup since Monday, the Times reported.

Coast Guard Chief Petty Officer Alan Haraf told the Times that, while it's still unclear, the danger levels are low.

"Any time you get any type of chemical in land or water, no one wants to see it," Haraf said. "We can't say for certain, but the danger seems pretty low."

EPA inspectors also concurred that the spill is unlikely to pose a long-term threat to the lake and have found amounts of oil off the shore.

The EPA said that the leak has been plugged since 9 p.m. Monday.

BP issued a statement following the spill and said that it will keep the area and those affected by the spill updated on the issue.

"BP is working closely with the U.S. Coast Guard, EPA and the Indiana Department of Environmental Management and will continue to keep the public and relevant authorities informed as events warrant," the company said.

The oil company said that the crews involved with the cleanup have recovered most of the visible oil on the surface by Thursday, MSNBC reported.

The leak was caused by a mechanical glitch, which discharged the crude oil in to the lake's cove.

While the drinking water has not been affected by the spill and no injuries have been reported, Illinois Sens. Dick Durbin (D) and Mark Kirk (R) requested to meet with BP's American Chief Executive Officer John Minge.

"This spill raises questions about the long-term safety and reliability of BP's new, expanded production at Whiting," the Senators wrote. "It is in all of our best interests ... to ensure that this greater processing capacity will do no harm to Lake Michigan."