I stumbled upon this phenomenon by mistake several years ago while swimming with some friends at the beach. It was a clear August night and the water was warm. We decided to go in for a dip, and to our surprise our splashing triggered an explosion of light! We couldn't believe our eyes.
They were dinoflagellates which are one of the more dominant species of phytoplankton in the Gulf of Maine. When disturbed certain dinoflagellates luminesce or glow through a chemical reaction known as biolouminescence.