On moonless nights, large and small boats line up along the dock to take visitors out to view the Bahía Fosforescente. Microscopic dinoflagellates glow when disturbed by movement, invading the waves with thousands of starlike points of light. The bay's glow has been diminished substantially by pollution—both light pollution from nearby communities and water pollution from toxic chemicals being dumped into the bay. (And, yes, the smoke-belching boats that take tourists to the bay are doing damage, too.) If you've seen the bioluminescent bay in Vieques give this one a pass. If not, you may find it mildly interesting. While it's not necessary to make a reservation—plenty of operators try to rustle up customers on the docks around sunset—Paradise Scuba runs the most reputable excursions in the area. Visit their dive shop for more information.