Dozens gathered inside the O’Brien Water Reclamation Plant in Skokie Wednesday for a belated ribbon cutting. And they all had to wear sunglasses.

The event marked the ceremonial opening of the ultraviolet light disinfection facility at the plant (which began disinfection about 60 days ago). This last stage of waste water treatment at the plant was a long time coming.

“We’re the last major city in the United states to do this—to disinfect the sewage that’s being dumped in the Chicago River,” said Sen Dick Durbin (D-IL) who pushed Water Reclamation District officials to adopt the treatment back in 2011.

As press and officials listened to speeches, stinky emerald green water flowed through tanks beneath their feet. The color comes from the UV lights meant to kill pathogens before the water flows into the Chicago River. Officials say that 450 million gallons pass through the facility each day

“Falling overboard in a boat into the Chicago River is a dangerous experience these days,” said Durbin. “That will change in the future and this is an important step forward.”

But don’t put on your bathing suit yet. Despite the anticipated improvement to Chicago River water, Metropolitan Water Reclamation District representatives still warn against swimming in it. 

Monica Eng is a WBEZ food and health reporter. Follow her at @monicaeng or write to her at meng@wbez.org.