Mosquito Bay – Vieques, Puerto Rico - Atlas Obscura
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Vieques, Puerto Rico

Mosquito Bay

World's most bioluminescent bay. 

At night, Mosquito Bay flashes green with an eerie ethereal light. Bright blue tracer lines suddenly appear in the water as small fish dart through the blackness. But this illumination has nothing to do with spirits or aliens: Mosquito Bay happens to be one of the most bioluminescent bodies of water in the world.

Bioluminescence is a form of natural light created by living organisms converting internal chemical energy into light. The light in Mosquito Bay is created by tiny organisms called dinoflagellates (specifically Pyrodimium bahamense or “swirling fire”), and Mosquito Bay contains an astonishing number - roughly 700,000 per single gallon of water. Although they’re microscopic, the effective size of the light they give off is a hundred times larger than their own bodies, and in great numbers they light up like an underwater aurora borealis.

Trapped by a curve in the Bay’s opening and fed by the surrounding mangroves, the dinoflagellates find Mosquito Bay a perfect home. Thought to bioluminesce as a defense mechanism - to attract predators that can ward off the small fish who eat them - dinoflagellates make light upon sensing any movement in the water, swirling out bright blue-green plumes that eventually diffuse back into the dark stillness of the Bay. This makes swimming in the Bay a truly astonishing - not to mention surreal - experience.

There are a number of outfits that will take people out to the bio-bay, but be sure to select one that uses kayaks not motor boats, and don’t wear bug spray, as gas and DEET both kill dinoflagellates. You are not supposed to swim here anymore, as it threatens the delicate balance of the bay and other biobays have already been severely damaged by visitors. In addition, be sure to visit on a night with no or little moonlight, as seeing the bioluminescence in near-total darkness is truly amazing.

Know Before You Go

Mosquito Bay is called Mosquito Bay for a reason, but don't wear bug spray with deet to visit, as it kills the bioluminescent organisms. You may itch for the next couple days, but it's more than worth it.

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