This is an image of a Carlsbad, CA beach during the 2005 red tide. The only image manipulation was the Photoshop Auto Levels command. The greenish-blue light is caused by millions (billions?) of microscopic organisms (Lingulodinium polyedrum) that bioluminesce when they are disturbed (as in a breaking wave). The effect is quite dramatic. The organisms also get washed to shore, so when you walk in the sand, your footsteps light up. If you are brave enough to enter the water at night, there will be a glow around you as you swim. Red Tides caused by L. polyedrum are not toxic.