|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.
For more details of results or earlier data, please contact us(external link).
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 monthly average biovolume of blue-green algae 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.
No health warnings are currently in place for the Waikato River.
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.
Routine monitoring of levels of blue-green algae 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 blue-green algae 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.
|21 Dec||no data||1.1||<0.1*||<0.1**||0.3||16.3||2.2|
|31 Jan||0.6||10.4||no data||no data||1.9||5.5||0.3|
*One sample collected 23 January, **One sample collected 23 January
A health warning is currently in place for Lake Waikare, Lake Ngaroto, Lake Whangape and Lake Waahi.
The Public Health Unit is 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) 349 3520.
If you have any enquiries about your local drinking water supplies please contact your local district or city council.