Cyanobacteria, commonly known as toxic algae, are naturally found in New Zealand’s river waterways, lakes, and coastal waters. While they are typically harmless at low concentrations, they can form harmful blooms when conditions allow, with some species producing toxins that can be potentially fatal if ingested. Often inhabiting the beds of rivers, lakes and the upper reaches of estuaries.
Toxic algae blooms are more likely to occur in clean water when river flow is slow or stagnant, temperatures are consistently warm, and conditions are stable. Floating (planktonic) cyanobacteria are present year-round in lakes and coastal waters but tend to increase during the summer months when water temperatures rise.
Council routinely monitors its cyanobacteria levels at recreation sites on the Maitai and Wakapuaka rivers, as well as Poorman Valley Stream in Isel Park.
Check weekly council monitoring and alert updates.
Please note that not all rivers are monitored. Please check out our Frequently Asked Questions and refer to our Fact Sheet for tips on identifying toxic algae.
If you're swimming, check out LAWA's Can I Swim Here? website.
