U.S. Water News Online
FAJARDO, Puerto Rico -- At night in a lagoon fringed with
mangrove thickets, kayakers set their paddles down and look to the
dark water for a secret of nature seen in few places.
You simply run a hand through the water, and a greenish glow
whirls off your fingers like radiant stardust.
Many who come here choose to jump out of their kayaks and watch
the bioluminescence stream off their hands and forearms as they swim
the breast stroke.
"Bioluminescence is actually very common, but not in the intensity
we find in these ecosystems," says guide Mark Donaldson, who has been
leading groups to the bioluminescent lagoon for eight years.
The mosaic of light under water, each tiny dot of it resembling a
firefly, is produced by microscopic plankton that create light
through a chemical reaction when disturbed.
The tiny organisms, known as dinoflagellates, feed on blue-green
algae that flourishes in the saltwater lagoon, making their
concentrations higher than in regular seawater.
Visitors reach the enclosed lagoon by making a half-hour paddle
from a marina in the eastern town of Fajardo through a canal that
winds through mangroves.
As the sun sets, bats can be seen swooping past overhead.
Some people say swimming through it is like sprinkling pixie dust
from every inch of the body.
"It was like beads of light that were going off the hairs on your
arm," says Carl Wolf, a lawyer from San Francisco visiting for the
Others call the experience ethereal, ghostly and peaceful.
When the bioluminescence is brightest, usually from August through
October, streaks of light from darting needlefish and stingrays can
be seen from the surface.
In other months, cooler waters generally decrease the
bioluminescence, but it still can be seen.
The effect is particularly striking when there is a new moon or
when the moon is obscured below the horizon.
Nevertheless, the glow is nearly impossible to capture in
photographs due to the low light.
Puerto Rico is uniquely blessed with three bioluminescent lagoons.
Tour guides on the outlying island of Vieques claim their spot at
Mosquito Bay is probably the brightest in the world.
There is another lagoon at La Parguera in southwestern Puerto
The closest to San Juan and its international airport is Fajardo's
Laguna Grande, or Grand Lagoon.
Interest in the tours has grown in recent years, and on many
nights dozens of kayakers squeeze through the canal leading to the
lagoon, sometimes colliding with others coming the opposite
Guides pause along the way, explaining the importance of mangroves
as nurseries for reef fish and often pointing flashlights into the
trees to expose huge iguanas perched on branches.
It is an environmentally sensitive spot, and for that reason
nearly all guides choose to lead the trips by kayak rather than
Most types of larger boats are prohibited in any case, and
kayakers with experience in the lagoons say they believe fuel that
leaks from outboard motors harms dinoflagellates and decreases the
Luis Mendez, who grew up near the lagoon and leads kayak tours,
says "every night the brightness is different" and that factors
including moonlight, rains and extended periods of sunshine all have
Regardless, he says, most visitors come away pleased, and some say
being immersed in that glow was among the best moments of their
If You Go...
BIOLUMINESCENT LAGOON TOURS: The tours include all necessary
equipment, including life vests and lights to help keep groups
Guides offer instruction on basic kayaking beforehand and also
give educational talks.
The microorganisms in the water are harmless, and the lagoon is
comfortably warm for swimming at night.
Visitors who have taken home a jar of the water have found the
glow quickly fades.
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