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Algal blooms

Blue-green algal bloom in Lake Ohakuri Blue-green algal bloom in Lake Ohakuri

Algae occur naturally in our rivers, lakes and streams, and flourish during hot and fine conditions. Most algae are harmless, but high levels of some species may be toxic and blooms may result in health warnings being issued.

Blue-green algae (also known as cyanobacteria or Anabaena) blooms are often found in waterbodies throughout New Zealand during our summer months. Blue-green algae have the potential to produce toxins that can affect public water supplies. Contact with these toxins can also cause skin irritations and other adverse health effects.

When blue-green algal cell counts reach unsafe levels, health warnings are issued advising people not to drink untreated water and to avoid recreational activities such as swimming, boating, or jetskiing that may result in skin contact.

Blue-green algal blooms are a common feature in some lakes in the Bay of Plenty region, with high levels recorded most years. Here in the Waikato region, blooms have been recorded in the Waikato River, Lake Taupō and several other lakes.

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.

Latest results - blue-green algae (cyanobacteria) levels

Click on a tab below to see the levels of blue-green algae (cyanobacteria) in recent water samples from sites along the Waikato River and in some of the region's shallow lakes. 

Waikato Regional Council also checks for blue-green algae as part of our routine monitoring of Lake Taupō's water quality, and if a bloom is detected in the lake then we will undertake additional monitoring.

  • Warning levels take into account both the number of cells and their size.  This is referred to as the "biovolume" of blue-green algae.
  • 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.
  • If there are public warnings health about a current algal bloom, there will  also be more information about it in our recent media releases.

If you'd like more details of these results, or you'd like to get earlier data, please contact us.

  • Routine monitoring along the Waikato River has continued in conjunction with several other agencies since late 2003.

    The key results from recent monitoring are shown below. The tableshows 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. Where there are exceedances above the guideline, the result for individual dates are shown.

    There are currently no health warnings in place for the Waikato River sites.

    Month Ohakuri Maraetai Karapiro Hamilton Tuakau
    August 2019 no data no data no data <0.1 0.9
    September 2019 no data no data no data <0.1 0.7
    October 2019 no data no data no data <0.1 <0.1
    November 2019 <0.1 <0.1 <0.1 <0.1 <0.1
    December 2019 3.24 0.9 <0.1 <0.1 0.91
    January 2020 <0.1 <0.1 <0.1 <0.1 0.32


Contacts for health or drinking water concerns

Public health units work closely with local councils to monitor drinking water standards.

If you’re concerned about health issues, call the Waikato District Health Board's Public Health Unit on 0800 800 977.

For queries regarding Lake Taupō or the upper Waikato River (from Taupō to Lake Maraetai) contact the Bay of Plenty District Health Board's Public Health Unit on 0800 221 555.

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

Frequently asked questions about blue-green algae

Lake Taupō algal blooms - December 2017

Lake Taupō had an algal bloom in late 2017 that resulted in a health warning. The warning has since been lifted, but you can read more information about the bloom and health issues in the FAQs below.