Short answer
The glow comes from dinoflagellates, single-celled plankton that give off a brief blue-green flash when the water around them is disturbed, according to Wikipedia and the University of Texas Marine Science Institute. It is seen only after dark, a dark night helps, and no operator can guarantee it. Two of our evening tours include a plankton stop: the Phang Nga Bay sea canoe tour from Phuket, from $115 per person, and the Krabi 7 Islands sunset tour, from $40 per person.
What is the glowing plankton?
It is a single-celled organism called a dinoflagellate. Wikipedia's article on dinoflagellates says that more than 18 genera are bioluminescent, that most of them emit blue-green light, and that the light comes as a brief flash of about 0.1 seconds when the cell is stimulated. NOAA's National Ocean Service defines bioluminescence as the production and emission of light by a living organism, using energy released by chemical reactions inside it.
The University of Texas Marine Science Institute compares it to a glow stick, not a glow-in-the-dark toy: the cell makes its own light from a chemical reaction that involves a compound called luciferin. Scientists think the flash is a defence. The institute says it may startle grazing predators or attract other predators to eat the grazers, and it adds that scientists do not completely understand why dinoflagellates make light.
Why does the water glow only when you move it?
Because the light is a reaction to being touched. Wikipedia says the flash is usually set off by mechanical disturbance, so a boat, a swimmer or a wave can make a blue sparkle appear on the sea surface. The University of Texas institute says the force of water flowing around the cells is enough, that people have reported blue streaks in the wake of ships for centuries, and that swimmers waving their arms or fish gliding past can make the water glow.
That is how our two tours describe it. On the Phang Nga Bay trip the glow shows when something moves the water, such as a paddle or a hand, and you look for plankton glowing around the paddle. On the Krabi trip it shows as you move through the water. Wikipedia adds that dinoflagellate bioluminescence is controlled by a body clock and occurs only at night, so a stop in daylight will show nothing.
Why does a dark night show it best?
Because the flash is faint and the eye needs time to adapt. The University of Texas institute notes that a human eye adjusted to the dark can see the flash from a single dinoflagellate, and a second article from the same institute, about Puerto Rico's bioluminescent bays, pictures reading by the light of the waves at night with no moonlight at all. We found no study that measures how the phase of the moon changes the glow, so we claim no rule. What the sources do show is that darkness is what lets the eye pick out the flashes.
Our tour information is practical about it: how bright the glow is depends on the moon, the tide and the water. NASA's table of the Moon's phase for 2026 puts the new moon on 9 November and 9 December 2026 and the full moon on 24 November and 24 December 2026. If your dates are flexible, the nights around a new moon are the dark ones. Our Phang Nga notes also advise keeping phone screens dim and flashes off during the night paddle so that everyone's eyes can adjust.
Can anyone guarantee that you will see it?
No. Wikipedia describes dinoflagellate blooms in general as unpredictable and short, and says luminescent dinoflagellate ecosystems are found in warm-water lagoons and bays with narrow openings to the ocean. The University of Texas institute says only a few places in the world have plankton dense enough for the bright blue glow of Puerto Rico's three bays, although dinoflagellates exist throughout the world's oceans. We found no study of how dense the plankton is in Phang Nga Bay or off Krabi.
So treat it as a bonus. Both of our tour listings say a sighting cannot be guaranteed, and both are full evenings in their own right: caves, a sunset dinner and the open sea in the dark on one, snorkelling, a sandbar and a beach barbecue on the other. If the plankton is your only reason to book, weigh that first. If it is one part of a good evening on the water, either tour is a reasonable bet.
How does the Phang Nga Bay canoe tour include it?
Our Phang Nga Bay Sunset Sea Canoe tour from Phuket is from $115 per person for about 10 to 11 hours, and the national park fees are included. Hotel pickup in Phuket is at about 10:00 to 11:15 am, the afternoon goes on canoeing into the caves and lagoons of Panak and Hong islands with a paddler, and dinner is served on the escort boat at sunset. After dark you paddle out with your guide to float a krathong and look for plankton glowing around the paddle.
The guides look for a dark, sheltered spot for the night paddle, and a paddler sits in each canoe, so you do not have to paddle yourself. You are back at the pier at about 8:00 to 8:30 pm and at your hotel at about 9:00 to 9:30 pm. Bring dry, warm clothes for the ride back; our notes say phones rarely capture the glow. The costs are in our Phang Nga Bay sunset tour price guide and the route in the travel guide.
How does the Krabi 7 Islands tour include it?
Our Krabi 7 Islands sunset tour is from $40 per person for about 7 to 8 hours by longtail boat from Ao Nang. The afternoon is snorkelling at Koh Yawasam and Koh Tan Ming, Chicken Island and the Tup sandbar at low tide, then a buffet dinner with BBQ on Poda Island at sunset. The plankton comes last: a swim of about 30 minutes in the dark off Koh Raeng, near Railay. The boat is back at the pier at about 7:00 to 7:30 pm.
Here you swim, so the glow shows as you move through the water. Jellyfish appear in some seasons, and long swimwear helps. The national park fee, 200 baht per adult and 100 per child, is paid in cash at the pier and is not in the tour price. Our Krabi 7 Islands price guide lists the extras, and the tour schedule gives the day hour by hour.
Which tour is the better bet for the plankton?
Neither, as far as we can tell: nothing we hold ranks the two for the glow itself, so choose by the rest of the day and by how you want to be on the water. The Phang Nga evening is the longer and dearer day, with caves, a floating krathong and a night paddle in which you look for the plankton from the canoe. The Krabi evening is cheaper, shorter and ends with a swim in the dark.
Not suitable on the Phang Nga tour: pregnant women, guests with heart conditions or other serious medical conditions, recent surgery or injuries, and anyone severely claustrophobic. Not recommended on the Krabi tour: pregnant women, infants under 2, and people with heart conditions or back, neck or spine problems. For either, send us your dates and hotel on WhatsApp. If the sea is unsafe, the operator moves the trip to another date or refunds it.
Practical checklist
- Treat the plankton as a bonus; neither tour can promise it.
- If your dates are flexible, look at the moon: the new moon falls on 9 November and 9 December 2026.
- Bring dry, warm clothes for the ride back after dark.
- Keep phone screens dim and flashes off during the night stop.
- On the Krabi tour, bring cash for the national park fee: 200 baht per adult, 100 per child.
Questions and answers
What is bioluminescent plankton?
Mostly dinoflagellates, single-celled organisms that make their own light by a chemical reaction. When the water around them is disturbed they flash blue-green for about a tenth of a second.
Can I see bioluminescent plankton near Phuket?
Our Phang Nga Bay sunset canoe tour from Phuket looks for it after dark. A sighting cannot be promised, because the glow depends on the moon, the tide and the water.
Do I have to swim to see it?
On the Krabi 7 Islands tour you swim for about 30 minutes in the dark. On the Phang Nga tour a paddler sits in each canoe and you look for the glow around the paddle.
What is the best night of the month to see it?
We found no study that measures it. Our tour information says the moon, the tide and the water all matter, and a dark night lets your eyes pick out faint flashes. Nights around the new moon are the darkest.
Will my phone photograph the glow?
Our Phang Nga notes say phones rarely capture it. Keep the screen dim and the flash off during the night paddle, so that everyone's eyes can adjust.
How much do the two plankton tours cost?
Phang Nga Bay sunset sea canoe tour: from $115 per person, national park fees included. Krabi 7 Islands sunset tour: from $40 per person, with the park fee of 200 baht per adult paid in cash at the pier.