Cyanobacteria (blue-green algae)

Cyanobacteria (commonly known as blue-green algae) are photosynthetic prokaryotic organisms that are integral parts of many terrestrial and aquatic ecosystems. In aquatic environments under favourable conditions, cyanobacterial cells can multiply and form planktonic (suspended in the water column) blooms or dense benthic (attached to the substrate) mats.

An increasing number of cyanobacterial species are known to include toxin-producing strains. These natural toxins, known as cyanotoxins, are a threat to humans and animals when consumed in drinking water or coming into contact with the skin during recreational activities.

Algal activity occurring in Northland

Samples collected at Lake Omapere outlet on 10 January 2019 returned with very high biovolume levels, however subsequent toxin results are below detection levels. Noticeable odour has been reported from neighbouring landowners and downstream on the Utakura River.

Another sample was collected on 16 January 2019 and is currently being analysed for cyanobacteria biovolume. Observations in the field suggest the bloom has partially dissipated on 16 January.

A sensor has been deployed in the Utakura river to monitor cyanobacteria levels and trial future monitoring methods. NRC will be collecting additional samples on behalf of Cawthron Institute to help calibrate field sensors to biovolume results.


Cyanobacteria Monitoring Report – 21 January 2019

Guidelines Location Biovolume (mm3/L) Date sampled

Surveillance (green mode)

  • Situation 1: The cell concentration of total cyanobacteria does not exceed 500 cells/mL.
  • Situation 2: The biovolume equivalent for the combined total of all cyanobacteria does not exceed 0.5mm3/L.

Lake Ngatu






Alert (amber mode)

  • Situation 1: Biovolume equivalent of 0.5 to < 1.8 mm3/L of potentially toxic cyanobacteria; or
  • Situation 2: 0.5 to < 10 mm3 /L total biovolume of all cyanobacterial material.




Action (red mode)

  • Situation 1: ≥12 μg/L total microcystins; or biovolume equivalent of ≥1.8 mm3/L of potentially toxic cyanobacteria; or
  • Situation 2: ≥10 mm3/L total biovolume of all cyanobacterial material; or
  • Situation 3: cyanobacterial scums consistently present.

Lake Waiparera

Lake Waiporohita

Lake Omapere








Monitoring sites

Map showing lakes monitored for cyanobacteria.

Frequently asked questions

Download our Cyanobacteria - FAQs document (PDF, 343KB) 

Report it

If you suspect a waterbody is experiencing a cyanobacterial bloom and there are no signs placed near the waterbody informing there is one – please contact the NRC 24hr Environmental Hotline to report it : 0800 504 639.