Algae creates 'toxic-looking' green water at Centennial Beach in Naperville

NAPERVILLE, Ill. (WLS) -- There's something in the water at a west suburban beach.

People have been asking why the water at Centennial Beach in Naperville looked so green. Now, with warm weather arriving, swimmers have also been wondering whether it's safe to take a dip.

Things certainly improved on Thursday, and that's good news for folks who've been there earlier in the week. One person told ABC7 Centennial Beach looked like the Chicago River on St. Patrick's Day on Monday.

"It was funny. It was a little radioactive green, you know?" Nathan Wagner said.

Centennial Beach looks more normal now, with folks eagerly and happily cooling down from Thursday's 90 degree heat. But, starting Memorial Day weekend, it looked quite green.

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"We were looking at it. We were saying, 'It's kind of a weird color, but maybe it's because we've never been to this pool before on Memorial Day.' So, it was kind of like, maybe that's the way it's supposed to look here, because it was a quarry or a reservoir or whatever it was," said Tiffany Wagner.

The bright green water raised enough eyebrows. Naperville's Park District issued a statement on Wednesday, declaring the former quarry safe for swimming and chalking the color off to algae growth due to the lack of rain and warming temperatures.

They explained that while the water there is chlorinated and re-circulated, it is not filtered like a typical swimming pool. Park district officials said they've been monitoring the water quality, and all the tests have come back normal.

"It was pretty toxic-looking. It was green. It wasn't slimy. It was just really green. I just figured the chemicals weren't just right," Barb Crittenden said.

Officials said they've been working to mitigate the algae to deter further growth. Those efforts appeared to pay off with the color starting to go back to normal.