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Questions and answers

Blooms of blue-green algae are often found in some waterbodies in the Waikato region during periods of warm, calm weather. High levels of blue-green algae make it unsafe for people to drink untreated water and to have recreational contact in or on waterbodies (swimming, boating, jetskiing). This page has information and answers to common questions about blue-green algal blooms

Microscope photo of blue-green algae Anabaena planktonicaOn this page: Algal blooms in our regionWhat we are doingQuestions and answers Still need to know more?

Algal blooms in our region

Blooms of blue-green algae are often found in waterbodies throughout New Zealand during our summer months 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. When blue-green algal cell counts reach unsafe levels, health warnings are issued advising people not to drink untreated water or to have recreational contact in or on affected waterbodies (swimming, boating, jetskiing).

Find out who to contact when a health warning is in place for information on drinking water concerns

What we are doing

Waikato Regional Council has been collecting samples to identify the types of algae present in large numbers in the Waikato River, Lake Taupo, and other Waikato shallow lakes.

Our monitoring in the summer of 2002/03 identified the blue-green algal species Anabaena in samples collected down the length of the Waikato River. Algae are naturally present in the River at all times and are mainly comprised of harmless diatoms. However, blue-green algae bloomed to high levels due to the hot and sunny weather.

Blue-green algae are known to have the potential to produce toxins that can affect public water supplies. These toxins can also affect recreational users of water by producing skin irritations and other adverse health effects.

For more information on algal blooms in the Waikato region, check out our latest media releases and monitoring results.

Questions and answers

What are blue-green algae?

Blue-green algae are microscopic organisms that are naturally present in waterbodies, and like plants grow in response to light and nutrients. Blue-green algae are also called ‘cyanobacteria’.

Are blue-green algae common?

Yes, it is common for blue-green algae to be present in the Waikato River, Lake Taupo and our shallow lakes, but they are not usually present in the Waikato River and Lake Taupo in large numbers. Blooms normally occur in standing water like ponds and lakes, rather than freely flowing waterbodies such as rivers and streams. We find them in the Waikato River because they grow in the hydro lakes upstream of Cambridge.

What do blue-green algae look like?

The Anabaena forms long chains of cells but these can only be seen under a microscope. They can be present in water in high numbers and still not be visible to the eye. The microscope photograph at the top of this page shows a sample of Anabaena planktonica taken from the Waikato River.

What is the problem with this type of algae?

Blue-green algae have the potential to produce toxins which can affect the health of humans and animals.

What causes this type of bloom to occur?

Blooms like this are often triggered by fine, warm and settled weather.

Has this type of bloom occurred before?

A bloom of blue-green algae was documented in the Waikato River in 1998 (Lake Maraetai) as well as in the summer of 2002/03. Similarly a bloom occurred in Lake Taupo in early 2001 as well as in 2003. Blue-green algal blooms have also been observed previously in several of the small lakes including Lakes Waahi, Ngaroto, Kainui and Hakanoa.

Can this type of bloom happen again?

Such blooms can be expected to occur in future when suitable conditions occur.

How often are you testing blue-green algal levels?

Following the blooms of summer 2002/03 we have continued monitoring in both the Waikato River and the shallow lakes. We generally monitor the Waikato River sites more frequently during summer (e.g. weekly) than during winter (e.g. monthly). The shallow lakes are monitored monthly during summer and every two months during winter.

How toxic/dangerous are these blooms?

Toxins were detected in samples collected from the Waikato River during the summer of 2002/03. However, toxin levels were much lower than the drinking water standards. Monitoring at Lakes Waahi and Hakanoa also showed that toxins were present in these waterbodies in the first part of 2003.

For more information on the potential health effects of blue-green algae, see Health Canada’s website.

Will blue-green algae affect fish and the taking of fish?

It is thought that fish and other animals living in the water could accumulate any toxins if present. Currently the risk of toxicity associated with these types of blue-green algal blooms is not known. For further advice you should contact the Public Health Unit.

For more information on the effects of blue-green algae on fish, see Health Canada’s website.

What impact might blue-green algae have on animals?

There have been recorded cases of animals being affected by stock drinking water with high levels of blue-green algae. Currently the risk of toxicity associated with these types of blue-green algal blooms is not known.

For more information on the effects of blue-green algae on animals, see Health Canada’s website.

Is there anything we can do to get rid of blue-green algal blooms?
No. We can only wait for them to take their natural course, and monitor them closely in the meantime.

Still need to know more?

Check out the latest monitoring results for:

  • the Waikato River
  • Lake Taupo
  • other lakes in our region.

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

For other enquiries about blue-green algal blooms, see our list of contacts.