City officials in Clive now know what caused a portion of Walnut Creek to turn bright green.

The water sample collected on Tuesday showed traces of cyanobacteria, which can produce the cyanotoxin microcystin, the Thursday news release said.

However, the sample collected was within the allowable range for safe water recreation.

The concentration of the microcystin was 2.9 ug/L. The Iowa Department on Natural Resources posts beach advisories for concentration levels greater than 20 ug/L and the Environmental Protection Agency's Health Advisory Level is 8 ug/L.

MORE: How to keep your children, pets safe from blue-green algae

Because the bloom is ongoing and there could be areas in the water where microcystin are more concentrated, the city recommends people and pets stay out of the discolored water until the algae bloom subsides.

City officials reached out to the Iowa Department of Natural Resources on Tuesday morning after a Clive resident posted a photo of the green creek on Facebook.

MORE: Iowa uses less restrictive standards than EPA guidance for blue-green algae toxins

The testing to determine the presence in the water was done at a lab at Des Moines Water Works, Clive Assistant City Manager Pete DeKock said. Samples were collected by partners at Drake University.

Janet Gastineau, a DNR senior environmental specialist, told the Register the agency traced the green water back to a lake in the Country Club development.

"We have reached out to them with an offer of technical assistance and I also referred them to Polk County Soil and Water Conservation District, who administers the Walnut Creek Watershed program," Gastineau said.

While Country Club Lake isn't owned or maintained by the city, it is a major part of the Walnut Creek watershed and can impact conditions downstream, DeKock said.

The city has not tested water in various parts of Country Club Lake, the release said. The city has shared the test results with the Country Club Home Owners Association, the DNR, and the Iowa Department of Public Health.

"City staff have made visual observations on the creeks and drainages that flow into Country Club Lake," De Kock said. "The water flowing into the lake at those points doesn't have the strong green color like the water flowing out of the lake currently has."

Gage Miskimen is a news reporter mostly covering West Des Moines, Waukee, and Clive for the Register. Reach him at gmiskimen@dmreg.com or 515-284-8234. Follow him on Twitter @gagemisky

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