Known as a 'red tide' by day, the microalgae Noctiluca scintillans, known as 'sea sparkle' emits a bioluminescent blue glow when disturbed at night. Over the last week, residents of Hobart, Tasmania, have been treated to a light show on the Derwent River, mostly around the South Arm Peninsula, as the dinoflagellate bloom has washed ashore. The bloom can be deadly to fish if it accumulates and gives off ammonia as the microalgae die.