Mayor Rahm Emanuel on Wednesday demanded a “full accounting” from BP after an oil spill apparently caused by a malfunction at the company’s Whiting refinery.

The U.S. Environmental Protection Agency has characterized the leak as minor and said there was no apparent impact on Lake Michigan, which supplies drinking water to the city and suburbs.

But Emanuel said he’s taking no chances about a lake he called “our Yosemite Park, our Grand Canyon” and the source of Chicago’s recreation and drinking water.

“There was a leak the other day. They’re calling it minor. I expect a full accounting to the public. . . .  I want a report on what happened, how it happened, why did it happen, how much happened and how do you prevent it from ever happening again,” he said.

“Chicago’s water was rated No. 1. I don’t want anything to ever endanger it. We’re investing in it. I want to make sure BP is a good corporate citizen next door in Indiana,” he said. “Like petcoke, which is a byproduct of that facility, we need to make sure . . . environmental policies we’re investing in . . .  are not rolled back because there’s a facility in Indiana that endangers the water quality of Lake Michigan that all of us rely on a daily basis, all seasons — from drinking water to our beaches to our recreation.”

Responding to a request for comment on Emanuel’s demand for a “full accounting” from BP, company spokesman Scott Dean wrote in an email: “BP continues to make progress in responding to an incident Monday at the Whiting Refinery.

“Crews have recovered the vast majority of oil that had been visible on the surface of a cove-like area of Lake Michigan and on the shoreline between the refinery and a nearby steel mill. They have used vacuum trucks and absorbent boom to contain and clean up the surface oil. Responders also manually collected oil that had reached the shore,” the statement said. “Monitoring continues in coordination with the U.S. Coast Guard, EPA and the Indiana Department of Environmental Management. BP and federal agencies are assessing the shoreline to determine what, if any, next steps are required in the response.

“BP continues to work to calculate the amount of oil discharged into the lake. This work involves estimating how much oil was released into the refinery’s cooling water system, water treatment plant and ultimately into the lake.”

Last year, questions were raised about whether City Hall was slow to respond to the mounting anger about petcoke on a Southeast Side, which has been Chicago’s dumping ground for decades because of Emanuel’s decision to abolish the city’s Department of Environment shortly after taking office.

At the time, the mayor placed the blame on the shoulders of former Mayor Richard M. Daley — without uttering the name of his predecessor and political mentor.

 “We hadn’t done anything as a city in the last nine years knowing full well this [Whiting] plant was being built. We’re catching up to what we should have done when Indiana took action,” he said then. “We were caught, as a city, allowing a company to take advantage of a regulatory loophole with our guard down flat-footed. And our neighborhoods and our children and our families were adversely effected.”

Emanuel initially ruled out a ban on petcoke in favor of regulations that, a community leader warned, did not go far enough to contain the ugly byproduct of the oil refinery process coating Chicago’s Southeast Side.

He has since introduced an ordinance that would prohibit new petcoke facilities from opening in Chicago and prevent existing facilities from expanding.