Cyanobacteria Toxic Algae

Cyanobacteria, more commonly known as 'toxic algae', are naturally present in New Zealand river waterways, lakes and marine water. It only becomes a problem when an increase in high concentrations forms blooms. Not all cyanobacteria species produce toxins, which can be potentially fatal if ingested. It is found living on the bed of rivers and lakes and in the upper reaches of estuaries, but can also occur in slow-moving water in rivers.

Toxic algae is generally found in clean water but can grow when river flows are low and stable and temperatures are consistently warm. Planktonic ('floating') cyanobacteria is present all year in lakes and coastal waters but generally increases over summer with warmer temperatures.

Council routinely monitors its cyanobacteria levels at recreation sites on the Maitai and Wakapuaka rivers and informs the community when action needs to be taken. Planktonic cyanobacteria monitoring is also undertaken at the Modellers Pond, Tahunanui as part of a project to manage water quality in the pond.


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Blue-green algae levels have increased due to warm settled weather. Keep children and dogs away from the river and its margins where they may come in to contact with algal mats. 

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.