Scientists have collected samples from algae blooms found during an inspection of Lake Taupō swimming sites this weekend.
Algal mats and surface water bloom samples were taken from beaches at Kuratau, Mission Bay, Motutere Bay, Hatepe, Halletts Bay and Whareroa South.
They'll be analysed by Waikato Regional Council scientists to determine whether any are toxic.
The council said the results should be available this afternoon.
In the meantime people are being urged to avoid algae-affected areas; signs are up at the six beaches concerned.
Contact with the algae mats could cause skin rashes, stomach upsets and respiratory symptoms.
The toxic algal species often multiply to high levels during periods of warm, sunny weather.
In lakes they can form extensive green to black-coloured mats that settle on rocks and the lake floor. Significant clumps sometimes break off and float free, collecting on the water's edge.
Meanwhile, organisers of this weekend's Ironman 70.3 Taupō event made a last-minute decision to cancel the swimming portion of the race.