Tests on the algae believed to have killed two dogs which were playing in the Silver Stream at Mosgiel have confirmed it is toxic.
The algae Phormidium, which flourishes in low flows and warm weather, was discovered in the stream last week.
Otago Regional Council staff sent samples of the algae to the Cawthron Institute in Nelson, which confirmed last week it was the cyanobacterial algae Phormidium and more recently that it was toxic.
ORC director of environmental information and science Dr John Threlfall said the results showed the form of algae discovered was toxic enough to warrant the warnings to keep dogs away from the stream.
"It is not very toxic, but it is not OK.
"It is wise to keep dogs out [of the stream]."
The council was still waiting on the test results from the contents of the stomach of one of the dead dogs.
Algae had also been spotted in small areas of the Kakanui River, but no warnings had been put up as it was not widespread and in more remote areas, he said.
"There isn't blanket coverage like the Silver Stream, which is next to an urban area and where people walk their dogs all the time."
Flows continued to be low in many coastal Otago rivers so people should assume the algae was in those rivers, Dr Threlfall warned.
