The red tinged water spreading along the Napier Coast has been confirmed as an algae bloom.
The natural phenomenon turning areas of Hawke's Bay water various shades of brown, purple and red, is due to a non-toxic algae known as Akashiwo sanguinea, meaning 'red tide' in Japanese.
The bloom, commonly seen in Tasmania and off the California and Florida coastlines, is most likely caused by consistent rain in Hawke's Bay over recent weeks.
Algae blooms occur when there is a rapid increase or accumulation in the population of algae.
Hawke's Bay Regional Council is taking samples over the next week to ensure the bloom poses no risk to human or animal health.
A flyover by council staff revealed the bloom stretches from Te Awanga to Wairoa.
The bloom is also causing more foam in the surf zones along the Napier Coast.