You are not permitted to download, save or email this image. Visit image gallery to purchase the image.
In a social media post labelled as "important information" the council described a slick floating at the northern end of Lake Hayes, near the recreation reserve.
"Our science team have identified that the green discoloration may be cyanobacteria," the statement read.
Staff are sampling and testing, and will have more information in a few days time.
"But for now it’s best to take a precautionary approach and stay out of the lake."
Dogs should also be kept out, the council advised.