Dr. M. W. Johnson, Professor of Marine biology,gives the answer to the riddle of why the Gulf of California is called "The Vermilion Sea".
The real cause for the color of the water is not the silt coming down from the Colorado River, but rather the presence of billions of tiny microscopical one-celled animals, which are classified under the name 'Noctiluca' more specific 'Noctiluca miliaris'. Some of these produce light, hence the name Noctiluca. These are spherical protozoa, about one milimeter in diameter of a faint pink color and possess a single, short, thick, flagellum. When they float near the shores, often in inconceivable numbers, they give the ocean the appearance of diluted catsup. At night when agitated by the waves, the minute dinoflagellates emit tiny flashes of light, and the sea takes on a magic glow, appearing at times like a spectacular pyrotechnic display, especially when the waves strike partly submerged rocks or floating objects.
The Gulf of California is not the only part of the ocean which at times turn red. Dr. W. E. Allen, who was the Scripps Institution biologist *, described occurrences of red water, one in LaJolla Bay, and three along the coast of Washington. He counted as many as 3,000,000 individual dinoflagellates in a quart of water.
* Died 1947 - Age 73.