La Parguera's bioluminescent bay

What bioluminescence is

The glow is produced by microorganisms called dinoflagellates. When the water is disturbed, they respond with a bluish flash. Just run your hand through the water and watch the light follow it.

It isn't constant or guaranteed: it depends on how many organisms there are, how dark the night is and the condition of the water.

Puerto Rico has three

Only a handful of bays in the world glow year-round, and Puerto Rico has three: Mosquito Bay in Vieques, Laguna Grande in Fajardo and La Parguera, in Lajas.

When to go

• Moonless nights or a waning moon. The darker the sky, the more the glow stands out.
• After dark. Tours leave once night has fallen.
• Clear skies. Rain and wind reduce visibility.
• Book ahead on weekends and in high season.

What to expect

It doesn't look like the heavily saturated photos you see online. It's a soft blue glow that appears wherever the water moves: in the boat's wake, around a paddle, or in your hands. Going in with realistic expectations makes the visit much better.

How to visit

There are two main ways:

• By boat: trips from the waterfront, comfortable and short. The most common option.
• By kayak: closer to the water and quieter. Some operators use clear-bottom kayaks.

Tips

• Wear clothes you don't mind getting wet and bring a dry change.
• Don't put on bug spray or sunscreen right before getting in the water: the chemicals harm the organisms.
• Keep your phone away for the first few minutes — the camera almost never captures what your eyes see.
• Ask the operator whether swimming is allowed on your date; conditions and rules can change.