Blue moon? 

How about blue ocean? 

Westshore residents and curious passers-by were treated to a natural light show on Saturday night when the ocean off the seaside Napier suburb turned blue. 

The natural phenomenon was captured beautifully on video by Codee Mavis Daley-Wilkins. 

The blue light occurs when bioluminescence is present in the water, usually from an algae bloom of plankton. 

The sea will glow but usually only when it's disturbed by a wave breaking or a splash in the water at night. 

Calm and warm sea conditions are usually needed as well for the phenomenon to occur. 

Saturday night's sea conditions were just that, a far cry from the swells that pummeled Hawke's Bay's east coast in the last few weeks of March during a prolonged period of bad weather.