According to the Los Angeles Times today, San Diego County is experiencing a “Red Tide.” See:
During a red tide, the sea water appears to have a reddish-brown tinge during the day. Not too exciting. During the night, however, the water appears to have a bluish glow instead. And that is pretty neat.
The colorations are due to a group of microorganisms called dinoflagellates. These are single-celled protozoa, often photosynthetic like their algae cousins. Ceratium, shown here, is in this family. Many members of this family are capable of bioluminescence, which is the property that gives off the characteristic glow of the red tide.