Bioluminescent Bays, Caves, and Parks: What Causes the Glow and Where to See It

Nature has given us some pretty incredible things—and creatures that glow in the night are at the top of the list. Here’s why bioluminescence happens and where you can travel to see it.

A boat of tourists floats through the water of New Zealand's Waitomo Glowworm Caves. A guide is standing in the boat pointing to the ceiling where many many small blue lights shine like a starry night, but it's inside the cave

New Zealand’s Waitomo Glowworm Caves are famous for their bioluminescence.

Corin Walker Bain

The phrase “glow-in-the-dark” might conjure memories of gimmicky children’s toys. But in the natural world, some organisms dazzle with their ability to produce light. This trait is known as bioluminescence, and it makes for a magical travel experience you won’t soon forget.

What is bioluminescence?

Visible only at night, the ethereal glow that is bioluminescence results from a reaction involving two chemicals—luciferase and luciferin—that can be witnessed in a variety of species. While some fish, shrimp, squid, and jellyfish have this ability, it is easiest to see in single-celled aquatic organisms called dinoflagellates that emit blue light when they are disturbed (say by an oar or a boat). A few land organisms, like fireflies, glowworms, and certain fungi, are also bioluminescent. The glow serves different purposes, like warding off predators, attracting prey, or communicating.

Where is bioluminescence commonly found?

Bioluminescent organisms live primarily in warm marine waters. Dinoflagellates tend to be most numerous in shallow bays and lagoons, where narrow openings prevent them from flowing away. By comparison, bioluminescence is rare on land and virtually nonexistent in fresh water, though scientists are still trying to understand why.

Is swimming in bioluminescent waters safe?

Swimming is allowed in certain bioluminescent bodies of water. However, some species of dinoflagellates can be toxic to humans. Be especially wary of algal blooms, which are an overgrowth of dinoflagellates. Experiencing marine bioluminescence from a boat or while paddling in a kayak is the safer bet.

Where in the world can you see bioluminescence?

Puerto Rico
Puerto Rico boasts not one, not two, but three dinoflagellate-rich bioluminescent bays. Laguna Grande in the town of Fajardo is the closest to the capital city of San Juan. You’ll be rewarded with an even more spectacular display, however, if you journey to Mosquito Bay on the island of Vieques. The bay is only accessible by kayak. La Parguera, in the city of Lajas in the southwestern corner of the main island, is the only one of the three bays where swimming is permitted.

Tomales Bay, California

Forty miles north of San Francisco is Tomales Bay, part of the Point Reyes National Seashore, where dinoflagellates give the water an otherworldly glow. Several companies offer guided nighttime kayak tours in late summer and fall, when the dinoflagellates are most abundant.

Ha Long Bay, Vietnam

Ha Long Bay in the northeast province of Quang Ninh in Vietnam is a UNESCO World Heritage Site on account of its limestone formations, but it’s also one of the top places in the world to see bioluminescent waters.

Great Smoky Mountains National Park, Tennessee and North Carolina

One of nature’s great bioluminescent spectacles takes place yearly at Great Smoky Mountains National Park, which straddles Tennessee and North Carolina. During a two- to three-week period in May or June, members of one special firefly species, Photinus carolinus, synchronize their patterns of flashing lights to attract mates. The park holds a lottery for special viewing nights of the phenomenon near Elkmont, Tennessee.

Waitomo Glowworm Caves, New Zealand

The famous Waitomo Glowworm Caves on the North Island of New Zealand harbor large colonies of bioluminescent fungus gnat larvae. Commonly known as glowworms, they cling to the walls of these caves, resembling stars shining in the night sky. Boat and walking tours to see their magical displays are available year-round.

Nathalie Alonso is a journalist based in New York City. Her work has also appeared in National Geographic, Outside, Refinery29, and Well+Good, among other publications.
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