During the warmer months, there can be potentially toxic blue-green algae present in our lakes and rivers.

There is reduced capacity to monitor for algal blooms over the Christmas and New Year period, so it’s important to know the signs of algal bloom to reduce your chances of becoming unwell.

“Algal blooms can develop rapidly and unpredictably and can sometimes produce toxins that are harmful to people and animals,” says Toi Te Ora Public Health, Te Whatu Ora Medical Officer Dr Gregory Evans.

Dr Evans suggests avoiding contact with the water if it looks discoloured, has an unusual smell, has green or brown particles suspended in it, or if scum or leathery mats of algae are on the surface or the bottom of the waterway.

“These blooms have the capacity to release toxins into the water which can cause skin rashes, stomach upsets and visual problems for anyone who has contact with the water.

"They can also affect the nervous system causing numbness, difficulty with breathing, and asthma attacks.”

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 can build up along the edges of lakes or rivers. It’s important parents ensure children avoid contact with these as they may be toxic.”

If you think you’ve been in contact with an algal bloom; shower and change your clothes as soon as you are able to, even if you don’t have any symptoms.

You should seek medical advice from your GP if you become unwell after having contact with recreational water.

Dogs are also at risk of serious illness if they consume or have contact with toxic algae or algal mats that accumulate in and around rivers. They should be kept away from the water if it looks like there may be a bloom.

There are currently health warnings in place due to algal blooms for Lake Ōkaro, Lake Maraetai and Lake Ohakuri.

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