For several Centuries, sailors have told stories of so called "milky seas." These 'milky seas' seemed to be glowing a dim white light. According to the log of the S.S. Lima as it sailed off the coast of Somalia 11 years ago, they were surrounded by waters that appeared as a field of snow or clouds in all directions. Scientist have been able to go back and look at satellite pictures at the time of this voyage and were able to find pictures confirming the glowing sea. Scientist say that this glow is caused by bioluminescent bacteria. One might ask how many bioluminescent bacteria would it take to light up the seas? Well if one were to cover the earth in a 4 inch layer of sand and then count all of the individual grains of sand in that layer, thats how many it would take. These glowing seas typically only last a few days are usually found in the Indian Ocean.
Scientist hypothesize that the bacterium Vibrio harveyi is responsible for this bioluminescence. There are dinoflagellates that will give off light as well. These organisms however must be physically stimulated to produce a brief flash of light. V. harveyi seem to give off a continuous light on their own. One hypothesis that is mentioned for the bacterium to continuously glow is to attract fish so they can enter their guts and live there.
The article and a minute long video can be found here.