Algal bloom has been found off the Napier coast at Marine Parade.
Hawke's Bay Regional Council's marine sampling identified the bloom last week and said the bloom is a is a reddish-brown colour that can resemble muddy water.
Samples taken by regional council staff have been analysed by Cawthron Institute which has identified very high levels of an algal species called Alexandrium catenella.
This is a dinoflagellate species that produce toxins, and can cause paralytic shellfish poisoning when affected shellfish are eaten. The sampling confirms current warnings issued by Ministry for Primary Industries (MPI) against consuming shellfish from the Hawke's Bay area.
"We often see algal blooms after periods of heavy rain," says Senior Scientist Coastal Quality Anna Madarasz-Smith. "As the freshwater moves off the coast, it pulls deeper water up which can feed algal blooms".
It is not known how long the bloom will last.