A portion of the Chicago River turned turquoise this weekend and it wasn’t on purpose

CHICAGO — While Chicago annually dyes its river green for St. Patrick’s Day, officials are investigating why the Chicago River turned a pretty shade of turquoise on Sunday.

As first reported by The Chicago Sun-Times, a portion of the river at Wolf Point turned a bright shade of greenish-blue. The color faded Sunday night.

The city’s Department of Water Management and the Metropolitan Water Reclamation District of Greater Chicago are investigating what caused the river to turn two different colors, but one official tells the Sun-Times they believe it was due to natural environmental changes.

“The discoloration is not due to outfill, but caused by a combination of the storm, seasonal vegetation changes and other naturally occurring circumstances,” water department spokeswoman Megan Vidis said.

Despite the City of Chicago’s stance, the river’s strange colors have garnered concerns among environment groups. Margaret Frisbie, director of Friends of the Chicago River, told the Sun-Times she fears the coloring could be due in part to the weekend’s heavy rainfall that caused sewers to overflow into the Chicago River.

“Sadly, when it rains we get a lot of sewer drainage in the river,” Frisbie said. “It’s not good, it’s harmful to the fish and to people’s health.”

When it rains, water drains into the storm sewers and comes into contact with sewage on its way to be treated. In 2015, WGN reporter Eric Runge found that the sewer overflow was causing high levels of bacteria in the river. The Metropolitan Water Reclamation District told Runge that they were making plans to clean up the Chicago River.

Since then, they have added new new equipment at O’Brien Water Reclamation Plant in Skokie that disinfects the Chicago River’s bacteria-ridden water. Plus, the City of Chicago has been testing “trash-skimming” boats to clean debris off the river surface.

This is the second time in two weeks that the Chicago River has made local headlines. A little over the a week ago, an oil spill occurred on the on the South Branch of the river. The cause of the oil spill remains a mystery.