Scientists have collected samples of algae blooms found during an inspection of Lake Taupō swimming sites this weekend.
High Algae levels had forced the closure of beaches in Taupo and the cancellation of the swim leg of the Taupo Ironman 70.3 over the weekend.
The council said the results should be available soon.
In the meantime people are being urged to avoid algae-affected areas; signs are up at the six beaches concerned.
Contact with the algae could cause skin rashes, stomach upsets and respiratory symptoms.
The toxic algal species often multiply to high levels during periods of warm, sunny weather.