Mosquito Bay

Mosquito Bay on the island of Vieques holds a Guinness record as the brightest bioluminescent bay recorded anywhere, and the reason is its shape: a narrow mangrove-fringed lagoon with a bottleneck mouth that traps the dinoflagellates inside and concentrates them in extraordinary numbers. On a dark night the effect is unmistakable - paddle blades trail blue fire, fish leave comet streaks under the kayak, and water poured from a hand falls in sparks. Tours go by kayak or electric boat with guides who know the lagoon and the rules that keep it healthy.

What you actually see

• The paddle glow - every stroke lighting the water blue-white.
• Fish trails - streaks under the boat as fish scatter.
• The mangrove rim - the enclosed lagoon that concentrates the organisms.
• Vieques by day - wild horses, empty beaches and the old naval lands turned refuge.

When to go

The bay glows year round, and the deciding factor is moonlight - trips around the new moon are dramatically brighter, and operators schedule accordingly. Book well ahead for new-moon weeks. Rain does not stop trips and can even help by keeping the sky dark.

Honest expectations

Swimming in the bay is banned - sunscreen, insect repellent and body oils harm the organisms, and the ban is enforced. Photography is difficult: phones almost never capture it, and guides ask for lights off, so plan to simply watch. Getting to Vieques takes a ferry from Ceiba or a small plane, both of which can be disrupted; build in a buffer day. Bring bug spray for before the trip and apply it far from the water.

Nearby

Vieques's beaches, the wildlife refuge on the former naval lands and the town of Esperanza.