Red colouring in the sea along the coast of Hawke's Bay has been confirmed as an algal bloom.
Hawke's Bay Regional Council says testing shows it's a non-toxic bloom called Akashiwo sanguinea (Japanese for red tide).
The council says the bloom is quite common in Tasmania, California and Florida and may be linked to persistent rain in Hawke's Bay over recent weeks.
The bloom, which varies from light brown to dark purple, stretches from Te Awanga to Wairoa.
The council will continue taking samples to ensure the bloom remains non-toxic and no risk to humans or animals.