San Diego's coastline has been lit up by a natural blue glow.
People have flocked to the coastline to see the natural light display in the ocean, which according to scientists is caused by a red tide.
The red tide is created by algae filled with microorganisms called phytoplankton that light up when they are jostled.
Photos of the aqua coloured light, referred to as bioluminescence have been posted to social media.
he light reacts with movement such as crashing waves and is thought to be a way of warning predators.
During the day, the algae is a red colour.
According to Scripps biological oceanographer Peter Franks, the red tide is most visible during the day between 11 a.m. and 1 p.m.
The glow was first forecasted on Monday and has continued throughout the week. It was most visible from La Jolla to Encinitas.
Scripps Oceanography say it's unclear how long the red tide will last.
Previous events have lasted from one week to a month.
They added that the Bioluminescent displays are best viewed two hours after sunset.
The last red tide in San Diego was in September 2013 and lasted a week.
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