There are places in the world where diving into the water on a moonless night is like diving into a sea of sparkling stars. The warm seawater lights up at your touch and leaves streaming light in your wake. If you are very fortunate, even your footprints will burst into rings of soft, glowing light as you walk along the damp sand.
Bodies of water rich in bioluminescent microorganisms can be found wherever salt water is deep, sheltered, and rich with nutrients. Narrow-mouthed bays which open up into calm seas are ideal. However, only a few places in the world are blessed with these perfect conditions.
Puerto Mosquito (also known as Bioluminescent Bay), Vieques, Puerto Rico
Mosquito Bay can be found on the small island of Vieques, just off the eastern shore of Puerto Rico. It is probably the best known bioluminescent bay in the world.
The still, undisturbed water of Mosquito Bay is home to the world's highest concentration of dinoflagellates, with 720,000 of these tiny microorganisms per gallon of water. Each individual bioluminescent flash from these microorganisms lasts only 1/10 second, but together, they light up the water in a vivid electric blue which can be seen for miles around. As a result, Mosquito Bay may be the brightest bioluminescent bay in the world.
Puerto Rico also has other bioluminescent bays in Parguera and Fajardo. However, the popularity of these bioluminescent bays is also threatening their continued survival. Garbage, fuel spillage, and other pollution from surrounding development has reduced the concentration of dinoflagellates in these areas to just 10% of that of Mosquito Bay. To make matters even worse, local light pollution is drowning out the more subtle illumination from these bays.
For now, the Vieques Historic and Conservation Trust has protected Mosquito Bay by keeping most of the region undeveloped. The bay is still surrounded by mangrove trees, just as it was when the Spanish first arrived and discovered an unearthly light which, they believed, was the work of the devil. They tried to choke off the bioluminescence by dropping boulders in the channel leading to the ocean. This concentrated the dinoflagellates in the bay and made the light even brighter.
Kayaking is permitted in the bay. Swimmers must be part of guided tours. The best time to visit this, or any other bioluminescent bay, is at the dark of the moon.
Halong Bay, Vietnam
On the other side of the world, the bioluminescence of Halong Bay is subtle. You won't be able to see it at all until all the boats turn off their power and lights at around 11 pm. Even then, you won't see much more than a shimmering sparkle to the water, until you dive into it and the water erupts into a brilliant electric blue around you.
Halong Bay also offers over 3,000 limestone islands to explore, many of them with extensive caves, grottos, and enclosed lakes. Hotels are available on Tuan Chau and Cat Ba, while other islands support floating fishing villages. The seafood here is exceptional. Beautiful beaches are everywhere.
In 2009, Halong Bay was on the final list of nominations for the world's 7 natural wonders. It has been a UNESCO World Heritage Site since 1994, both for its beauty and its unique geology.