Lan Ha Bay Bioluminescent Plankton Sunset Boat Trip, Cat Ba

Lan Ha Bay at sunset and the floating village

Lan Ha Bay, off the eastern shore of Cat Ba Island, is part of the Cat Ba archipelago that joined Ha Long Bay's UNESCO World Heritage listing in 2023. By late afternoon most day boats have gone home, and the bay becomes quiet: the limestone towers turn gold, fishermen return to their rafts and the water settles into glassy calm.

From the pier at Cai Beo the boat passes the floating fishing village, one of the oldest settlements in northern Vietnam, with its colourful raft houses and fish cages. The light at this hour is ideal for photos. Is Lan Ha Bay worth visiting in the evening as well as by day? Yes, it feels like a different place, softer and more intimate, and this is the only time of day the plankton can be seen.

Monkey Island

Monkey Island, a short ride from Cat Ba Town, has a sandy beach backed by forested rock where a troop of wild macaques lives. The boat stops in front of the island for about an hour of golden-hour swimming in warm water, while you watch for monkeys along the shore. Sightings are very common, but they are wild animals and never guaranteed.

Depending on the tide the boat may not be able to come right up to the beach, so you swim the last stretch to shore. If you want to climb the rocky path to the viewpoint, bring shoes in a waterproof bag. Keep food, bags and sunglasses close and do not feed the monkeys: they are curious and quick to grab loose belongings.

Swimming with bioluminescent plankton

After sunset the boat moves to a sheltered beach away from town lights. Here the water holds tiny marine plankton that give off a blue-green glow whenever the water moves. As you swim, every stroke and kick leaves a trail of sparks, and handfuls of water seem to fill with stars. It is a natural phenomenon and difficult to capture in photos, so this is a moment to enjoy with your own eyes.

The brightness changes from night to night with the season, the tide and the moon; darker nights usually show the glow best, and the warmer months bring the strongest displays. The plankton is always present, but it may be fainter than in pictures. Plan on about an hour here, with life jackets for anyone who wants extra support in the dark water.

Cat Ba Town, the pier and dinner

Around 20:00 the boat heads back to the pier, and by 20:30 or 21:00 you sit down to a family-style dinner at a local restaurant next to the harbour: fish, spring rolls, chicken and tofu, with a vegetarian option. The food is not halal-certified, but seafood and vegetable dishes are plentiful; tell us about any dietary needs when booking.

Cat Ba Town is the island's small harbour town and the best base for Lan Ha Bay. How to get to Cat Ba from Hanoi: about three hours by road via Hai Phong with a short sea crossing, or by ferry from Tuan Chau in Ha Long. After dinner we drive you back to your hotel. The best time to visit Lan Ha Bay for night swimming is from May to October, when the sea is warm.