A health warning has been issued by the local Medical Officer of Health for Lake Rotorua due to a potentially toxic algal bloom.

During the warmer months lakes and rivers can be affected by blooms of blue-green algae which can lead to a release of toxins into the water.

“These algal blooms can readily move from one part of the lake to another. The algae can also quickly multiply to dangerous levels and lake users need to be vigilant before having any contact with the lake water,” says Dr Phil Shoemack, Te Whatu Ora Medical Officer of Health for Toi Te Ora Public Health.

“Algal blooms can sometimes produce toxins that are harmful for people as well as animals. It is best to avoid contact with the water if it looks discoloured, has an unusual smell, has green or brown particles suspended in it, or if you can see scum or leathery mats of algae on the surface or on the bottom of the waterway.

“These blooms have the capacity to release toxins into the water which can cause significant ill-health to anyone who has contact with the water. The toxins can affect the nervous system causing numbness and difficulty with breathing, and also sparking asthma attacks. Contact with the water can also cause skin rashes, stomach upsets and visual problems.”

Lakes are typically dominated by free-floating algal blooms, while rivers are more prone to algal blooms that grow in mats attached to rocks at the bottom. They can also build up at the shoreline.

“Algal mats and scum may also accumulate along the edges of lakes or rivers so it’s especially important that parents ensure that children avoid contact with these as they may be toxic,” says Dr Shoemack. You should seek medical advice from your GP if you become unwell after having contact with the recreational water.

Dogs are also particularly at risk of serious illness if they consume or have contact with toxic algae. They should be kept away from the water if it looks like there may be a bloom.

They may also eat algal mats that accumulate in and around rivers.

A health warning is issued by Toi Te Ora Public Health if recreational water monitoring results provided by Regional Councils show a site to have high levels of blue-green algae.

Find information on local health warnings on the following channels:

• List of health warnings - Toi Te Ora Public Health website
• Follow Toi Te Ora social media channels at Facebook, Instagram, and X
• Signage at locations (erected by local councils)
• Land, Air, Water Aotearoa website