The first time I saw waves light up in beautiful colours as they crashed onto the beach I thought someone had slipped me some acid. It's real, though. Bioluminescent phytoplankton cause this spectacular light show, and wow, someone's surfing it.
Red tides exist all over the world, and they are caused by large-scale algae blooms. Some red tides, however, like those found in southern California contain a certain type of phytoplankton called lingulodinium polyedrum that emit little bursts of light when agitated. When a ton of those little guys are gathered into a small area and are all agitated at once by a crashing wave or a slicing surfboard, the effect looks like something out of Disney's Fantasia. It's simply breath-taking.
Red tides are often responsible for massive fish deaths, and its effect on humans who directly contact it is not entirely known. Anecdotally the CDC says that swimming in red tides may cause "irritation of the eyes, nose and throat, as well as coughing, wheezing and shortness of breath. Additional evidence suggests that people with existing respiratory illness, such as asthma, may experience these symptoms more severely." Hope this guy had a neti pot handy. [The Atlantic via The Scuttlefish]