“It could be a number of things, from an oil slick to bacteria or algae,” said Balthasar Buhidar of the Idaho Department of Environmental Quality, adding it could also be a combination of those things.
He said samples have been sent to a microbiologist for testing but results will take at least a week.
The globs appeared over the Memorial Day weekend, Buhidar told The Times-News. By Thursday the globs had changed to a rusty color and had accumulated on the banks.
They appear to have spread from the north bank to the south bank starting near Centennial Park and going downstream to Auger Falls, a distance of about 5 miles. He said he doubts they are oil-based because oil usually sits on the surface.
“This is through the whole water column.” he said.
Buhidar said he hasn’t spotted any dead fish, which would indicate the black globs are toxic.
“My first concern was for public safety,” Buhidar said. “But people didn’t seem to mind it. They were still boating on the river.”
The wastewater treatment plant for Twin Falls isn’t to blame, city spokesman Joshua Palmer said. He said the globs start upstream of the plant. Wastewater effluent can cause algae blooms with nitrogen and phosphorous loading.
Idaho Fish and Game biologist Doug Megargle said he hasn’t received any calls about the globs and the agency likely won’t get involved unless fish start dying.
Buhidar said the globs are dissipating at Auger Falls where the water starts churning.
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