East of Esperanza, Bahía Mosquito (Mosquito Bay) is also known as Bioluminescent Bay or Phosphorescent Bay. It's one of the world's best spots to have a glow-in-the-dark experience with undersea dinoflagellates. Tour operators offer kayak trips or excursions on nonpolluting boats to see the bay's tiny microorganisms that appear to light up when their water is agitated. Dive into the bay and you'll emerge covered in sparkling water. Look behind your boat, and you'll see a twinkling wake. Even the fish that jump from the water will bear an eerie glow. The high concentration of dinoflagellates sets the bay apart from the other spots (including others in Puerto Rico) that are home to these tiny organisms. The bay is at its best when there's little or no moonlight; rainy nights are beautiful, too, because the raindrops splashing in the water produce ricochet sparkles. Some of the best excursions to the bay are offered by Sharon Grasso of Island Adventures.

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