The warm summer weather has prompted a notable visible increase in various algal blooms on parts of Lake Rotorua and Lake Tarawera.
However, the latest test results from the Bay of Plenty Regional Council have not shown high levels of the potentially toxic blue-green algae.
The blooms were sighted and reported to the regional council by members of the public living on the Ngongotaha side of Lake Rotorua and by Te Toroa Dr/Kotukutuku Bay at Lake Tarawera.
The blooms are green and yellow and have an unpleasant smell. They have caused the water to discolour and in some areas formed a layer of scum on the surface.
The regional council undertakes regular water testing at the region's lakes to monitor both bacterial contamination and for signs of blue-green algae. Monitoring for blue-green algae has increased over summer.
It is also liaising with Toi Te Ora - Public Health Service over the state of the lakes and ongoing test results.
Toi Te Ora Public Health Service medical officer of health, Dr Neil de Wet said that so far this summer, levels of the potentially toxic blue-green algae had not been detected at a level that was a risk to health.
"However blue-green algal blooms can occur very rapidly and unpredictably, especially in these warm summer conditions. Therefore, as always, it is advisable for the public to check the water before using it. It's wise to avoid any areas where the water is discoloured, has surface scum or has an odour."
Regional council lakes operations manager, Andy Bruere, said the recent warm temperatures and the nutrients that ran into the lake were the likely cause of the algal blooms.
"Algae thrive on nitrogen and phosphorous and develop in warm, slow moving water bodies such as lakes. The weather we are experiencing would be the most likely explanation for the increase in bloom activity," said Mr Bruere.
"In addition, today's science is telling us that too many nutrients are entering the lakes from rural areas around the lake, sewage and even our famed geothermal activity.
"The sources and amount of nutrients entering the water differs for each lake, so the solution to preventing future blooms and achieving long-term sustainable water quality means different actions will need to be taken in each lake."
Last December, the regional council adopted rules that require rural landowners in the Lake Rotorua catchment to reduce the amount of nitrogen loss on their land from entering the lake. These rules will be notified for public feedback at the end of February.
"We are committed to working with our local communities to help address these issues and ensure that our lakes are in a better state to hand down to future generations. We all want the same thing - clean lakes - and must work together in order to achieve that."
Visit www.rotorualakes.co.nz to find out what is being done to protect and restore water quality in the Rotorua Te Arawa lakes.