On the beaches of Southern California, a phytoplankton called Lingulodinium polyedrum is responsible for a spate of red tide. Massive algal blooms like this make the water ruddy during the day, but disrupting the microorganisms at night results in bursts of electric blue bioluminescence.
Credit: @io9 on Twitter
This is absolutely beautiful. I have seen bioluminescent phytoplankton once at a Virginia beach but it was bright green at night. Spooky and amazing.