Booking choice: The small-group day cruise, from $32 per person. Check dates Tour details
Lan Ha is the part of the bay people come to for the water. It has more than 130 small beaches among about 400 limestone islands, and the lagoons behind them are calm enough for beginners in a kayak. Most day boats from Ben Beo build the day around one swim stop and one paddle.
What you can actually do depends on the season, the tide and the rules of the month. Here is the honest version: where you swim, how warm and deep the water is, the jellyfish, the kayak situation in 2026 and the glowing plankton.
The quick answer
Swimming is part of most Lan Ha itineraries, at beaches such as Ba Trai Dao and Van Boi or straight off the boat. The water is warm (27 to 30 C) from May to October and cold in winter; jellyfish peak from April to August. Kayaking rules in Lan Ha changed several times since late 2024, and some boats now row you in bamboo boats instead: check the listing's itinerary for 'kayak' or 'bamboo boat' before you book.
Can you swim in Lan Ha Bay?
Yes. Swimming from beaches and from the boat is part of most Lan Ha itineraries, and the water is calm and sheltered by the islands.
The day boats from Ben Beo plan the day around a beach or a quiet islet. On the small-group day cruise lunch is at Ong Cam islet with a swim and a jump off the boat, then beach hopping at Ba Trai Dao; the Cat Ba full day also swims at Ba Trai Dao. Overnight cruises from Tuan Chau add a swim stop in Lan Ha and sometimes a pool on deck.
Swim where the crew anchors and nowhere else: the channels carry boat traffic, and Ba Trai Dao has no facilities at all. Bring water shoes. Rocks, shells and dead coral are sharp on several beaches.
Where are the best beaches and swim stops in Lan Ha Bay?
Ba Trai Dao (Three Peaches) and Van Boi by boat, Monkey Island's Cat Dua beaches from Ben Beo, and the Cat Co beaches you can walk to from Cat Ba town.
The boat beaches are the good ones. Ba Trai Dao is the pick, but it is tide-locked: the sand is exposed for only a few hours a day.
| Beach | How you get there | What it is like | Watch for |
|---|---|---|---|
| Ba Trai Dao | Boat only, on day tours | Small white cove by three islets, knee-deep and calm | Covered at high tide; sharp rocks |
| Van Boi | Boat only, near Ba Trai Dao | Very quiet, clear water | Currents at the edges; dead coral |
| Monkey Island (Cat Dua) | About 15 to 30 min by boat from Ben Beo | Two beaches and a viewpoint | Monkeys can be aggressive; don't feed them |
| Cat Co 1, 2, 3 | Walk 15 to 20 min from Cat Ba town | Free; 1 is shallow, 3 has more waves | Busy at weekends; seafront works |
Ba Trai Dao, Cai Beo floating village and a kayak, with an up-to-10-guest option.
Check dates for the small-group day cruiseHow warm is the water in Lan Ha Bay?
About 27 to 30 C from May to September, 28 C in October, 25 C in November and 19 to 20 C from January to March.
Those are weather2travel's monthly averages for Ha Long Bay, which shares the same water. April is the turning point at about 23 C: fine for a quick dip, cold for a long swim. By late September the sea holds 26 to 28 C, and it stays swimmable well into October.
For a swim-centred trip, the sweet spots are May and early June, and late September to October: warm water, calmer seas than midsummer. Our best time to visit guide has the full month-by-month table.
Are there jellyfish in Halong Bay and Lan Ha Bay?
Yes, mainly from April to August. Blooms in the north are milder than in southern Vietnam, and box jellyfish are recorded in the central and southern seas, not here.
Most of what turns up is harmless or gives a sting that burns for a while, but ask the crew before you jump in: they see the water every day. In season, a rash guard or thin long-sleeved swim top does most of the work. Avoid swimming at dawn, at dusk and after heavy rain.
If you are stung, localvietnam.com's advice is to rinse with seawater (not fresh water), pour on vinegar for at least 30 seconds, lift any tentacles off with a card rather than your fingers, then soak in hot, not scalding, water for 20 to 45 minutes.
How deep is Halong Bay?
Shallow for open sea: the average depth is about 5 to 10 m, with channels of 15 to 29 m, according to the Ha Long Bay Management Board.
Depth isn't the issue for swimmers; the tide is. The bay has one high and one low tide a day, with a range of about 1.9 to 4.6 m, so a beach can vanish and a cave tunnel can close within hours. That is why crews shuffle the order of stops, and why Ba Trai Dao and the Ba Ham tunnels are timed around low water.
Life jackets are standard on every kayak session, whether or not you swim well. On the beaches you are on your own, so weak swimmers should stay in the shallow, calm coves such as Ba Trai Dao.
A full day from Cat Ba with kayaking through three caves, a Ba Trai Dao swim stop and a bike ride in Viet Hai village.
Explore the Cat Ba full day Tour detailsCan you still kayak in Lan Ha Bay in 2026?
Kayaking rules in Lan Ha changed several times since late 2024; some boats now row you in bamboo boats instead. Check the listing's itinerary for 'kayak' or 'bamboo boat' before you book.
Cat Hai district suspended all kayaking in Lan Ha from 15 November 2024 until proper regulations were in place. In 2026, one cruise operator reported a fresh suspension from 1 February, with rowed bamboo boats at Dark and Bright Cave instead, while other 2026 guides say kayaking runs again from Ben Beo. Bhaya Cruises wrote in June 2026 that cruise guests could paddle in the Ao Ech area.
Every tour on this site lists kayaking in its 2026 itinerary; on some days crews switch to a rowed bamboo boat. The bamboo boat is a local rower taking a small group through the same cave tunnels: slower, no effort, and better for photos. The kayaking rules update follows the notices as they change.
- Only with a licensed operator: independent kayak rental off the beach is not allowed in the bay.
- Life jackets are required on every session.
- Children usually paddle from about 4 or 5 years old, in a double kayak with an adult.
- Sessions last about 45 to 90 minutes.
Where do you kayak in Lan Ha Bay?
In the lagoons: Ao Ech (Frog lagoon), Ba Ham with its three tunnels, Tra Bau, the Dark and Bright Cave and the water around Van Boi.
- Ao Ech (Frog lagoon): a wide, enclosed lagoon on the 6-star Azura and Rita itineraries, enclosed by cliffs.
- Ba Ham lagoon: three lagoons linked by low tunnels you can pass only around low tide. The best paddle in the bay when the timing works.
- Tra Bau: the kayak stop on the Hanoi day cruise and an option on the Rita itinerary.
- Dark and Bright Cave (Sang Toi): on the Ha Long - Lan Ha border, the stop where crews most often switch to bamboo boats.
- Bright, Dark and Bat caves: the three-cave paddle on the Cat Ba full day from Ben Beo.
Keep an eye on the cliffs: the catbaday crew says you may spot a Cat Ba langur, one of the rarest primates on earth, with about 90 left in the 2024 count.
Can you see glowing plankton in Lan Ha Bay?
Yes, on some nights. The glow is strongest from roughly May to October, on dark, calm nights away from town lights and big ships.
Bioluminescent plankton light up blue when the water moves: a paddle stroke, a hand trailed over the side. Lan Ha's dark lagoons are the best place for it around Cat Ba, according to localvietnam.com, and a moonless night a day or two after rain gives the best odds. A full moon washes it out, and winter sightings are rare and faint.
The 2-day kayak and Viet Hai trip builds it in: after a day boat from Ben Beo, you paddle from 19:00 to 20:30 to find the glow, then sleep in a bungalow in Viet Hai village inside the national park. It is nature, so no one can promise a bright night.
A night paddle among glowing plankton, then a bungalow in Viet Hai village and a morning bike ride.
Explore the 2-day kayak and Viet Hai trip Tour detailsFrequently asked questions
Can you swim in Halong Bay, Vietnam?
Yes. Cruise boats from Ha Long anchor at swim stops along the route and many continue into Lan Ha for a beach or a jump off the boat. Swim only where the crew anchors, and plan on cold water from December to March.
Are there dolphins in Halong Bay?
Rarely, and no tour can promise them. A Gulf of Tonkin cetacean survey (Raffles Bulletin of Zoology, 2003) found dolphins and porpoises only at low densities. Tuoi Tre reported dolphins seen repeatedly in Quang Ninh waters, Ha Long Bay included, in 2024, and rare pink dolphins off Do Son in Hai Phong in 2026: news because it is unusual.
Do I need to be a strong swimmer to kayak?
No. Life jackets are required on every session, the lagoons are calm, and double kayaks are common. Keep phones in a dry bag; the Cat Ba day tours we list supply one.
Is it safe to swim at night?
Only with your guide's approval. The water is cooler after dark, and the plankton tour on this site is a kayak paddle, not a swim.
Ready to book
Choose your trip
Free cancellation up to 24 hours before on every option. Prices are from-prices in USD and move with the season.
Lan Ha Bay Small-Group Day Cruise & Kayak
Up to 10 people on the small-group option
Cat Ba Full Day: Boat, Kayak & Viet Hai Bike
- Hotel pickup and drop-off on Cat Ba Island
- Boat trip with kayaking through Bright, Dark and Bat caves
- Swim stop at Ba Trai Dao beaches
2 Days: Lan Ha Kayak, Hike & Viet Hai Night
Kayak by day, sleep in a village inside the national park
