Safety measures for keep cancer-causing chemicals out of Lake Michigan ought to be virtually foolproof. The lake is not only the source of our drinking water, but also home to commercial fishing, shipping and a wide range of recreational activities.

But on Tuesday, a hazardous chemical — hexavalent chromium — started flowing into an Indiana tributary that in turn flows into Lake Michigan. Officials of the nearby Indiana Dunes National Lakeshore had to close three nearby beaches. Ogden Dunes, also nearby, closed its beach as well. A water treatment company had to shut its plant down until the water could be proved safe.

EDITORIAL


The cause? A failed expansion joint at U.S. Steel’s Portage, Indiana, facility, according to the company. That allowed wastewater carrying the chemical, which was the topic of the 2000 movie “Erin Brockovich,” to flow into the wrong treatment plant and in turn into Burns Waterway just 100 yards from where the waterway flows into Lake Michigan.

How does something as mundane and predictable as a leaky pipe joint let a hazardous chemical get into our water? Where were the backup safety measures?

Mayor Rahm Emanuel was right to condemn U.S. Steel’s “careless conduct” and call on the company to explain how it put so many people at risk. He also sought an assurance from the company that the leak wouldn’t be repeated.

After doing its own testing on water a mile from where the contaminated tributary flows into the lake, the Chicago Department of Water Management on Thursday found an elevated level of hexavalent chromium, but said it was well below federal safety standards. The department said the chemical has not reached city water intakes, and that city water remains safe to drink.

Also on Thursday, U.S. Steel said it had fixed the pipe, and the leak had stopped. But no one yet knows how much of the chemical flowed into the lake or how long the water must be monitored. More testing remains to be done. It’s also too soon to know what the long-term effect will be on the diverse flora in the national lakeshore.

At a time when environmental rules are under assault in Washington, Tuesday’s leak illustrates why federal environmental agencies, including the Environmental Protection Agency, must not be slashed, as the Trump administration wants to do. It is also a reminder that everyone from industry to local government has to be vigilant if we are to avoid future environmental disasters.