Vieques Mosquito Bay

The Bioluminescent Bay (also known as Puerto Mosquito, Mosquito Bay, or "The Bio Bay"), is considered the best example of a bioluminescent bay in the United States and is listed as a national natural landmark. The luminescence in the bay is caused by micro-organisms, dinoflagellates, which glow whenever the water is disturbed, leaving a trail of neon blue.

A combination of factors creates the necessary conditions for bioluminescence: red mangrove trees surround the water (the organisms feed off the dead leaves); a complete lack of modern development around the bay; the water is cool enough and deep enough; and a small channel to the ocean keeps the dinoflagellates in the bay. This small channel was created artificially, being the result of attempts by the occupants of Spanish ships to choke off the bay from the ocean. The Spanish believed that the bioluminescence they encountered there while first exploring the area, was the work of the devil ('El Diablo') and tried to block ocean water from entering the bay by dropping huge boulders in the channel. The Spanish only succeeded in preserving and increasing the luminescence in the now isolated bay.

Kayaking is permitted in the bay and may be arranged through local vendors. Swimming is allowed on limited basis through guided tours.