We have finally left Palmas del Mar marina in Puerto Rico, where we had been staying for the last three weeks. We took the first weather window after ten days of rain and squalls to motor to Vieques in the nearby Spanish Virgin Islands. The passage was rough, but fortunately short, only a few hours long. We dropped anchor in a creek leading to Puerto Mosquito, also called Bio Bay (so called because it is supposedly the bioluminescent capital of the world).

We waited until the night was sufficiently black, and then kayaked down the creek into the bay. Even in the creek, our paddle strokes created small swirls of light. Pretty good by our standards, but that was nothing, nothing, compared to what we found inside the bay. It was like we had crossed a magic line. The minute we entered the bay, the bioluminescence was multiplied a million-fold. The slightest motion evinced huge scintillating clouds of green light. It was most excellent.

I was dared by a certain reader to do two things: to jump into La Mina falls in El Yunque rain forest (man, that water was cold), and to swim in Bio Bay. We have now done both. Needless to say, I was the first one in the water. Despite what I expected, it was not creepy to slide into the pitch black water, but exhilarating. Each movement turned the water around me into green fire.

During the day, Puerto Mosquito is calm, shallow, and very murky. In other words, it’s your typical mangrove bay. The bay provides sanctuary for a number of species, such as pelicans, snook, mullet, mangrove cuckoo, herons, and rays. But by far the most well-known inhabitant of Bio Bay is Pyrodinium bahamense. It is a unicellular plankton with two whip-like tails, called flagella, that aid in movement. When agitated, this tiny life form emits a bright green flash of light, creating the glow in the water known as bioluminescence.

We have noticed bioluminescence in our wake before, but never in this volume. The reason for this concentration of glowing dinoflagellates results from several factors, which have conspired to create the perfect environment. Such factors include salinity, water depth and temperature, solar radiation, and slow circulation. The underwater fireflies have taken advantage of these perfect conditions, and multiplied. There are over 600,000 organisms in just one gallon of water.

After swimming for almost an hour, we got back in the kayaks, and paddled slowly home, some of the bioluminescence still clinging to our skin. It was one of the coolest experiences we have had on this trip, and certainly was the best night swim ever!