Algae bloom Camp Bay

Algal bloom in Camp Bay (Whakaraupo Lyttelton Harbour) 

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Over the weekend, a bright-coloured algal bloom appeared in Whakaraupō/Lyttelton Harbour. After receiving a public report, staff collected samples to identify the species and assess any potential risks to humans and fish.

Laboratory results later confirmed that it was formed by a species called Karenia longicanalis. This is a naturally occurring algae, which some people mistake for discharge or contamination because of its bright colour.

Impact on fish and humans

Karenia is free-floating marine algae (phytoplankton). Several species of Karenia are known to produce blooms around the world, including New Zealand.

  • Effects on fish: Karenia longicanalis can produce toxins that may be harmful to fish when blooms form. The toxin can damage sensitive gill tissue.
  • Effects on humans: This species is not known to be toxic to humans.

We have had no reports of fish death in Lyttelton Harbour at the time of the bloom in Camp Bay. 

Health warnings and risk assessment

When a marine algal bloom is observed, we visit the site and take samples. The results are then sent to Ministry for Primary Industries (MPI) and Te Whatu Ora to assess whether there is a risk to human health. If it shows that there is a potential risk to human health, a health warning will be issued. 

In the case of the bloom observed in Camp Bay, Ministry for Primary Industries (MPI) will not issue any health warnings as the results show that it does not present a food safety risk to humans. 

Causes of algal blooms in marine environments

These types of algal blooms are not uncommon this time of year and we have observed several already around Banks Peninsula. 

“Generally this type of bloom occurs during warm, settled weather,” said manager for water and land science Dr Elaine Moriarty.

A lot is unknown about the specific conditions that cause the different species of Karenia to bloom. Some possible causes could include: 

  • Natural environmental conditions: Slow water circulation or unusually high water temperatures.
  • Extreme weather events: Cyclones, floods, or droughts can trigger bloom.
  • Nutrient overload: Sometimes algal blooms are caused by “overfeeding”. This happens when nutrients (mainly phosphorus, nitrogen, and carbon) build up at a rate that "overfeeds" algae in the environment. Nutrient pollution from human activities can make the problem worse. This leads to blooms occurring more often. 

Duration and monitoring of algal blooms

How long an algal bloom takes to clear will depend on the wind, rainfall, sea state and circulation, and temperature in days after it appears. 

Once observed, our teams continue to monitor a bloom until it disperses 

Reporting algae blooms: If you see an algal bloom, phone us on 0800 765 588 or report an environmental incident using our online form.

We appreciate receiving these reports (including photos) from the public as they allow us to visit the site and take samples as quickly as possible.

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