Source: Auckland Council

Locals and visitors may see slimy algae – usually black or dark green in colour, in the sea and on beaches in the region this summer.

This could be the cyanobacteria Okeania spp. that has occurred during the last two summers. Last summer large quantities of the algae washed up on shore on Waiheke Island and Kawakawa Bay.

More recently, in October and November 2024, the algae has washed up on Waiheke Island and at Algies Bay, in Auckland’s north. In January 2025, the algae has washed up on beaches near Pine Harbour Marina in Beachlands. The algae could appear on other beaches around the region this summer.

Paul Klinac General Manager Engineering, Assets and Technical Advisory, reassures the public there’s no need for concern about the algae, but advises people avoid touching it.

“During summer, it’s common to see all types of algae blooms occurring. We are continuing to monitor Okeania spp. and are ready to act, if required.

“In the meantime, if you see the slimy algae around the region, please avoid contact with it as it could lead to skin, eye and respiratory irritations. Keep an eye on your dogs, as well, and ensure they avoid the algae.”

About cyanobacteria Okeania spp.

Generally, the drivers of cyanobacterial blooms are complex, and it is difficult to predict or explain where they may occur, as well as their size and duration.

This is because numerous environmental conditions need to be met to enable the rapid growth of the cyanobacteria – this includes calm weather conditions, plenty of light, warm seawater temperatures and sufficient nutrients to sustain their growth.

While we don’t know what causes it to bloom in different locations from year to year, the warm sea temperatures are likely contributing to the recurring blooms.

There is still much to find out about the ecology and toxicology of Okeania spp. However, we do know from previous observations in the Hauraki Gulf, and from overseas, that this grows in the shallow seabed area.

Because it is naturally widely distributed in low abundances and growing sub-tidally, it is impossible to remove it completely from the marine environment.

Staying safe at affected beaches 

The beaches where the algae are present remain open to the public but Auckland Council advises the following: 

• Avoid contact with the algae, including wading in affected areas, as it could lead to skin, eye and respiratory irritation 

• If you feel unwell as a result of contact with the bloom, contact your doctor, or call Healthline on 0800 611 116 

• Do not gather or take algae from the beach for things like using on your garden  

• Keep dogs away from the algae and any decomposing material which could cause a reaction 

• Do not gather or consume shellfish from the affected beaches. 

Frequently asked questions about cyanobacteria 

What are cyanobacteria? 

Cyanobacteria (or blue-green algae) are naturally occurring microscopic organisms that live in a range of aquatic environments, from near-pristine to those more impacted by land use. 

Are cyanobacteria harmful to humans? 

Some species of cyanobacteria (including Okeania spp. ) are known to produce toxins – collectively referred to as lyngbyatoxins – which could lead to skin, eye and respiratory irritations. 

Do cyanobacteria originate from outside New Zealand? 

No. Cyanobacteria are naturally occurring in New Zealand waters. 

Are cyanobacteria common in New Zealand waters? 

The cyanobacteria Okeania spp. occurs in low abundance throughout the Hauraki Gulf. Blooms of the filamentous cyanobacterium identified at the time as Lyngbya majuscula have been reported in various parts of the Hauraki Gulf particularly in the Omana Beach area.

There have also been reports of previous summer blooms at sites in eastern Auckland in the Hauraki Gulf (Musick Point, Eastern Beach and Howick) as well as sites in the Manukau Harbour (Kaitarakihi Bay) and at North Head in the Waitematā Harbour.

Some of the earliest records of Lyngbya spp. go back to surveys in the 1950s and in the 1970’s it was described as a seasonally dominant species on rock platforms around Motukaraka Island. Through the 2000’s there were regular occurrences of blooms around the Beachlands and Ōmana areas. 

Why is the cyanobacteria occurring now?

The drivers of cyanobacterial blooms are complex, and it is very difficult to predict or explain where they may occur, as well as their size and duration. This is because numerous environmental conditions need to be met to enable the rapid growth of the cyanobacteria (calm weather conditions, plenty of light, warm seawater temperatures and sufficient nutrients to sustain their growth), followed by the right conditions to dislodge blooms (ie stormy weather).

Once dislodged, factors such as the tidal conditions and wind direction need to be understood to predict where blooms may eventually be deposited. These requirements mean blooms most commonly occur during spring and summer, and are a natural phenomenon in shallow, productive coasts. It is likely that a perfect combination of conditions in recent months has resulted in the current washed up bloom on Waiheke Island and Algies Bay.

What impact does cyanobacteria have on the environment? 

Some cyanobacteria blooms can have serious impacts on aquatic ecosystems in general including potential toxic effects due to smothering and shading. However, there is a lack of research when it comes to the environmental impacts of Okeania spp. 

What research is being carried out into the cyanobacteria?

• Working closely with Auckland Council, Cawthron Institute has identified the dominant component of the cyanobacterial mats as Okeania. Dr Laura Biessy at Cawthron Institute has carried out some analysis to characterise the species responsible for these blooms on Waiheke Island and assess their toxicity.  However, there is a lack of research surrounding the ecology, toxicity and impact on the environment of benthic cyanobacterial species such as Okeania.
• Cawthron Institute recently published a study of shellfish collected from beaches on Waiheke Island that have been affected by Okeania blooms. They were tested for lyngbyatoxin-A (LTA) accumulation, and the results confirmed LTA had accumulated in marine snails, rock oysters and cockles collected near the algae mats. These results underline the need for further studies assessing the risks of human exposure to LTA through seafood consumption.
• Dr Biessy is currently trying to isolate and culture this species to enable future research, in particular the ecology of the species, its preferred growing conditions (temperature, salinity, nutrients, etc.) and habitat. These answers would allow us to predict when future blooms might occur and what could be done to mitigate these blooms.

MIL OSI