Bioluminescent Bay & Wildlife Preserve
It is a "Must See" when you are in Vieques, a "once in a lifetime experience". Bio-Bay in Vieques is unique. It is just spectacular.

The bioluminescence in Bio-Bay is microscopic one-celled organism called a dinoflagellate (Pyrodinium bahamense). They are part animal because they move around and part plant because they photosynthesize sunlight using chlorophyll. How or why do they glow? They emit a bright glow whenever they are agitated, or moved around. As a single cell organism, this built in defense mechanism can make them seem larger than the actually are (1/500") to predators. 

Because the viewing of Bio-Bay is affected by light, even the reflected light of the moon can dim an otherwise incredible experience. Therefore, there are times when it becomes less than desirable to venture out on the bay. It is best viewed during a New to Waxing or Waning moon, or before moon rise or after moon set. A full moon is not the best time to see the bio bay.

There are couple of different ways to see the bay, either by motorboat (for those who wish to stay dry) or by ecologically sound tours that are a lot closer to the water and are self-propelled in Kayaks. It's a much more hands-on experience and you can't help but get wet. These tours are very entertaining and informative as well.