State officials are trying to identify black globs that have formed in the Snake River in south-central Idaho.
Balthasar Buhidar of the Idaho Department of Environmental Quality says samples have been sent for testing but results will take at least a week.
Buhidar tells The Times-News that the globs appeared over the Memorial Day weekend.
They appear to have spread from the north bank to the south bank from Centennial Park to Auger Falls.
Buhidar says the globs could be anything from an oil slick to bacteria to algae, or a combination.
Officials say the globs by Thursday had changed to a rusty color and had accumulated on the banks.
Buhidar says he hasn't spotted any dead fish, and people are still boating.