Health New Zealand - Te Whatu Ora has issued a health warning for Okawa Bay in Lake Rotoiti 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.

Public health advice is to avoid any recreational activity that could result in significant contact with 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 Lynne Lane, Medical Officer of Health for the National Public Health Service.

“Algal blooms can sometimes produce and release toxins that are harmful for people, as well as animals, and can cause significant health issues for anyone who has contact with the water.

“The toxins can affect the nervous system causing numbness and difficulty with breathing, and spark asthma attacks. Contact with the water can also cause skin rashes, stomach upsets and visual problems.

“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.”

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 accumulate at the shoreline.

“Algal mats and scum may build up 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 Lane.

“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 and should be kept away from the water if it looks like there may be a bloom.

A health warning is issued by the local Medical Officer of Health if recreational water monitoring results provided by Regional Councils shows a site to have high levels of blue-green algae.

Find information on local health warnings on the following channels: