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Algal blooms in the Waikato region

Photo of blue-green algal bloom in Lake Ohakuri
Blue-green algal bloom in Lake Ohakuri

Algae occur naturally in our rivers, lakes and streams, flourishing during hot and fine conditions.

Most algae present in waterways are harmless, but high levels of blue-green algae may be potentially toxic.

In recent years blooms of blue-green algae have been reported throughout New Zealand due to favourable climatic conditions. Blue-green algal blooms are a common feature in some lakes in the Bay of Plenty region with high levels recorded most years. In the first few months of 2003, blue-green algal blooms were recorded in the Waikato River, Lake Taupo and several other lakes. In several cases this resulted in health warnings being issued. 

In early 2010 the Ministry for the Environment released new guidelines for measuring and assessing levels of blue-green algae in waterbodies.  Warning levels now take into account both the number of cells and their size.  This is referred to as the "biovolume" of blue-green algae.

More algal bloom information may be available in our media releases, and you can also find out more about algal blooms in our questions and answers page.

Latest results

For more details of results or earlier data, please contact us.

Waikato River

Routine monitoring has continued in conjunction with several other agencies since late 2003. The key results from recent monitoring are shown below.  

The table below shows the biovolume of cyanobacteria in samples collected recently from sites along the Waikato River. Results are in mm3/L. The guideline value for contact recreation is 1.8 mm3/L. Any results higher than the guideline are shown in bold. These results are provisional only. There may sometimes be delays with updating the details. The numbers below show the monthly maximum biovolume recorded at each site.







January 2019

0.8 1 0.9 <0.1


February 2019

<0.1 <0.1 0.5 <0.1


March 2019

<0.1 <0.1 <0.1 <0.1


April 2019 <0.1 <0.1 <0.1 <0.1 <0.1
May 2019 <0.1 <0.1 <0.1 <0.1 <0.1
June 2019 <0.1 <0.1 <0.1 <0.1 <0.1
July 2019 <0.1 <0.1 <0.1 <0.1 1.7
August 2019 no data no data no data <0.1 0.9
There are no current health warnings for the Waikato River

Lake Taupō

As part of our routine monitoring of the water quality of Lake Taupō, we will continue to be on the lookout for blue-green algae in the lake.  If a bloom is detected we will undertake additional monitoring.

Algal hotspots – lake arms

Side-arms of water-ways such as hydro-lakes, can have different conditions than those in the main lake including poorer flushing and higher temperatures. These factors can sometimes support rapid growth of algae resulting in very visible algae blooms, sometimes described as ‘pea soup’. For more information, please click here.

Other Waikato lakes

Routine monitoring of levels of cyanobacteria in several of the smaller lakes continues.  Hamilton City Council provides the results for Lake Rotoroa (Hamilton Lake) and Lake Rotokeao.

The table below shows the biovolume of cyanobacteria in samples collected recently from sites in shallow lakes in the Waikato region. Results are in mm3/L. The guideline value for contact recreation is 1.8 mm3/L. Results higher than the guideline are shown in bold. These results are provisional only.

Date Hakanoa Ngaroto Rotoroa Rotokeao Puketerini Waahi Waikare Whangape Kainui
24 Jul - 0.1 - - - - - - 2.9
8 Aug <0.1 - - - - <0.1 14.3 0.1 -
15 Aug - - <0.1 <0.1 - - - - -
28 Aug - - - - - - - - 10.7
5 Sep <0.1 - - - - <0.1 28.4 0.1 -
10 Sep - - <0.1 <0.1 - - - - -
26 Sep - - - - - - - - 2.0
2 Oct <0.1 - <0.1 - - <0.1 - 0.2 -
15 Oct - - <0.1 - - - - - -

A health warning is currently in place for Lake Kainui and Lake Waikare.


Contacts for drinking water concerns

The Public Health Units are working closely with local councils, including Hamilton City Council, to monitor drinking water standards.

If you’re concerned about health issues contact the Public Health Unit of the Waikato District Health Board on the freephone 0800 800 977. For queries regarding Lake Taupo or the upper Waikato River (from Taupo to Lake Maraetai) contact the Public Health Unit of the Bay of Plenty District Health Board on (07) 0800 221 555.

If you have any enquiries about your local drinking water supplies please contact your local district or city council.