In a statement Wednesday, Chicago Mayor Rahm Emanuel said the discharges from the steelmaker's Midwest finishing plant in Portage, Ind., USA, were the latest of what he called repeated violations of the plant's wastewater permits. 

"Chicagoans rely on Lake Michigan for our drinking water, as an economic engine and as a recreational asset. This Great Lake is our most precious natural resource and we must preserve and protect it, while taking steps to punish those who pollute it," said Emanuel. 

"We will not stand idly by as U.S. Steel repeatedly disregards and violates federal laws and puts our greatest natural resource at risk."

The lawsuit arises from two separate incidents, in which more than 350 pounds of chromium was discharged into the lake. The first incident occurred in April 2017; the other took place in October. 

You can read the mayor’s statement here. The Chicago Tribune has more coverage here.