Testing has revealed black algae washing on Waiheke shores is toxic. “Currently the algal bloom on some Waiheke beaches could lead to skin or eye irritation if you are in contact with the water,” said Dr David Sinclair, Te Whatu Ora’s Northern Region medical officer of health.

Caulerpa brachypus, which can spread rapidly and create dense mats, was found in July in Blind Bay and Tryphena Harbour. This was the first time the pest species had been detected in New Zealand.

The whale had earlier been spotted stranded.