A bio bay is a body of water that contains millions of micro-organisms, called “dinoflagellates”, that glow in the dark for a second when agitated. It is a rare, natural wonder that you can easily experience while visiting Puerto Rico. It is best seen on a dark night, try to go when it is moonless or close to it. It also is best on a warm night (summertime is brighter than wintertime, no rain is better than rainy days). But even on a less than ideal night, the bioluminescence will be visible. It is a fragile environment, that can be destroyed (as was the La Parguera bay) by excessive abuse from motor oil, sewerage, sunscreen, and bug repellent.
There are three bioluminescent bays (bio-bays) in Puerto Rico. One in the SouthWest – “La Parguera”, one on Vieques – “Mosquito Bay”, and the one in Fajardo – “La Laguna Grande”. Out of all three, Mosquito Bay is the brightest, and La Parguera is the least bright. La Laguna Grande in Fajardo is very bright, and it is convenient to do from San Juan and the main island.