Hon Mun Has Been Shut Since June 2022, and the Nha Trang Boats Go Elsewhere

Hon Mun became Vietnam's first marine protected area in 2001

The Hon Mun Marine Protected Area Pilot Project started in June 2001 after a long preparatory period. It was financed by the Global Environment Facility through the World Bank, by the Royal Danish Government through Danida, by IUCN and by the Vietnamese government, and it was the country's first marine protected area.

The line it drew encloses 160 square kilometres: the waters around Hon Mun and eight other islands lying up to 10 kilometres off Nha Trang. Roughly 38 square kilometres is land and 122 is water. The nine islands are Hon Tre, Hon Mieu, Hon Tam, Hon Mot, Hon Mun, Hon Cau, Hon Vung, Hon Rom and Hon Ngoc.

Khanh Hoa's People's Committee created the Hon Mun MPA Authority in March 2002 and approved a temporary zoning plan the same year. About 40 mooring buoys went in to keep anchors off the coral. The site later took the name Nha Trang Bay Marine Protected Area.

The reason for choosing this water was the coral. The biodiversity assessment done during the set-up phase recorded more than 340 coral species inside the area, the highest count in Vietnam, and 44 coral genera at Hon Mun itself, against 65 hard coral genera for Vietnam's south central zone as a whole.

The same assessment recorded the harder facts too. Reef fish status was described as very poor, sedimentation was rising and crown-of-thorns starfish were already killing reef-building corals. About 5,300 people lived on the islands inside the boundary, 95 per cent of them living off fishing, which is the arithmetic every rule since has had to work around.

Swimming and diving at Hon Mun stopped on 27 June 2022

In June 2022 photographs of bleached and broken coral at Hon Mun went round Vietnam and the province moved. On 21 June 2022 the standing committee of the Khanh Hoa Party Committee issued a conclusion accepting that the reefs had declined and ordering activity in vulnerable parts of the bay to stop, Hon Mun first.

The Nha Trang Bay Management Board issued its notice on 24 June. From 27 June 2022, swimming and diving in the Hon Mun area were suspended until further notice. Glass-bottom boats and boat tours went with them.

The conclusion named causes on two sides. Objective: climate change and two large storms. Subjective: gaps in state management, weak coordination between agencies, illegal fishing, dredging, unauthorised construction on the shore and pollution from tourism. Accounts of that same conclusion disagree on the storms, one naming 2017 and 2021 and another 2019 and 2021.

By 19 August 2022 the city had closed six of the seven dive points in the bay. On 7 November 2022 the provincial People's Committee issued Decision No. 3028, the overall plan to restore Nha Trang Bay to 2030, built around 16 tasks.

The suspension has outlasted every timetable put to it. A report on the Hon Chong reef dated 28 May 2026 still describes swimming, diving, glass-bottom boats and tourist activity as suspended inside the strict protection sub-zone, with the board patrolling and clearing crown-of-thorns starfish month by month.

The coral figures behind the closure, and the ones that disagree

Start with the survey that triggered it. In January 2022 the Nha Trang Bay Management Board surveyed the Hon Mun sub-zone and put live coral cover at 41.63 per cent in the northeast, 24.6 in the northwest, 14.5 in the southeast and 7.8 in the southwest.

Against 2015 the same account gives two comparisons that do not use those sectors. It pairs the northeast and southwest at 53.7 per cent in 2015 falling to 32.62, and the southeast and northwest at 52.2 falling to 11.15. The pairings cannot be reconciled with the four sector figures, so the sector figures are the ones to carry.

The long series is bleaker. Measured against a 1994 study, average coral cover across the bay had fallen about 7.2 percentage points to 22.8 per cent, and the area of coral from 754 hectares to 636.6. Institute of Oceanography monitoring from 2002 to 2015 had found the strictly protected areas stable while points outside them lost cover.

Published research is harsher. A study of 10 sites over the three years to 2019 found mean coral cover down 64.4 per cent, with site losses between 43 and 95 per cent, Acropora down 80.6 and Montipora down 82.3, and concluded that by the end of 2019 more than 90 per cent of the bay's corals were gone. Crown-of-thorns starfish stood at 4.2 per 100 square metres.

A 2025 remote-sensing study counts the loss in hectares instead: 191.38 hectares of coral disappeared from the protected area between 2002 and 2024, 125.06 of them by 2016 and 66.32 in the eight years after. Its authors attribute the loss to land-use change, warming and the starfish.

Enforcement was thin while this happened. In 2022 the board had one patrol vessel and six crew for more than 296 square kilometres of bay, and that March it fined a boat 12.5 million dong for fishing with electric guns north of Hon Rom, inside the strictly protected sub-zone.

Where diving runs instead: Hon Rom, and the four pilot areas of June 2024

Before the closure, 17 registered diving companies worked six dive sites at Hon Mun. That is the business the suspension removed in a single notice.

The board opened a temporary dive point in the Hon Rom area, and its terms are unlike anything Hon Mun ran. Dives are held to 15 to 20 minutes with one to three people in a group, and divers are told to stay 30 to 50 centimetres off the coral and not to touch, sit on or lever at it, dead colonies included.

On 12 June 2024 the provincial People's Committee approved a pilot reopening of recreational diving at four places, none of them Hon Mun: north of Hon Rua island, an artificial reef deployment area, northeast of Tri Nguyen island, and the water between Bai Tranh and Bai Soi on the east side of Tri Nguyen. It attached conditions on inspection, on criteria for choosing operators and on penalties for diving outside the scheme.

An earlier proposal had gone further. In August 2023 the board asked to reopen one site on the southern side of Hon Mun, conditional on a fresh Institute of Oceanography survey, with entry limited to divers holding international certification, capped numbers and round-the-clock patrols. It did not happen, and tourism at Hon Mun could not resume in 2024.

What has changed is the coral. An end-2023 survey put cover in the north and northwest of Hon Mun back at 30 to 50 per cent, on hard corals growing about a centimetre a year. Monitoring in early 2026 by the Institute of Oceanography, the coastal branch of the Vietnam-Russia Tropical Centre and the board found reefs recovering at 2 to 4 metres at Hon Chong, Hon Mun and Bai Cui, on the rubble the 2017 and 2021 storms left behind.

The bay charges a visit fee, and it stops at the protected core

Resolution 02/2025/NQ-HDND, passed by the Khanh Hoa People's Council on 15 August 2025 and in force from 25 August, sets a fee for visiting the Nha Trang Bay scenic landmark. It replaced a resolution of 13 December 2016 that had charged for visiting the Hon Mun Marine Reserve.

The fee is per person per trip and excludes accident insurance. Route 1 to Hon Mieu is 6,000 dong. Routes 2, 3 and 4, to Hon Tam, Hon Tre and Hon Mot, are 8,000 each. Route 5 to Hon Mun is 10,000. Route 6, all routes combined, is 40,000.

Who pays is narrow: tourists moving by inland waterway craft inside the bay boundary. Exemptions run long and include children under six, people with disabilities, residents of Khanh Hoa and anyone aged 60 or over. Children from six to under 16, school and college groups and poor households pay half.

The boundary is the part worth reading. The fee applies inside the bay as defined by Decision No. 738/QD-UB of 21 March 2005, from Mui Ke Ga to Mui Cu Hin, and then carves out the strict protection sub-zones: the whole east and southeast of Hon Tre, from Dam Bay out to Hon Mun, Hon Noc and Hon Cau, plus the water within 300 metres seaward of each island's shoreline at the lowest tide.

So the protected core is not simply closed. It sits outside the charge the rest of the bay pays. Collection began on 25 September 2025 at four points: the Nha Trang tourist wharf, the Phu Quy and Institute of Oceanography inland waterway wharves, and the Ana Marina park. The board keeps 80 per cent of the take and pays 20 to the state budget, and from September 2025 to 30 April 2026 the fee raised more than 5.8 billion dong.

What Vietnamese law asks of a business that takes tourists underwater

Vietnam has no diving statute. It handles recreational diving as a tourism product with a risk to the life and health of the tourist, under the Law on Tourism of 2017 and Decree 168/2017/ND-CP, signed on 31 December 2017 and in force from 1 January 2018.

Article 8 lists what qualifies. Clause 3 names diving underwater alongside paddling through rapids, jet skis, board riding and parasailing towed behind a boat. Once a product is on that list, Article 9 attaches five duties.

The operator must post warnings and guidance on climate, weather and health. It must have a rescue plan, rescue staff in place, prompt response to an incident and communication maintained with guests throughout. It must use trainers, technicians and guides with expertise appropriate to the activity. It must publicise the safety rules and give technical instruction before the activity starts. And it must supply safety equipment meeting standards, show guests how to use it and supervise that use.

Article 10 adds the paperwork. The business must notify the provincial tourism department in writing at least 15 days before it starts operating. The department then has 15 days to check the notice and publish on its information portal the list of businesses meeting the requirements, and it may demand corrections before operations begin. Tour operators that subcontract these activities must use only suppliers that meet them.

No public register of licensed Vietnamese dive operators is readable, and which registers can be read logs what each source returns and on what date.

Our own list is short and says less than people expect. The Nha Trang operator list holds 6 businesses, read on 21 August 2026. All 6 are published by SSI in its register of affiliated centres and all 6 publish a website there. None appears in the IKO or VDWS registers and none is a Green Fins member. The town field the register files them under names Khanh Hoa province, which is the province Nha Trang sits in rather than a mistake.

Water temperature and the two seasons of Nha Trang Bay

Nha Trang Bay covers about 507 square kilometres and holds 19 coastal islands; the inner bay is about 130. Two monsoons cross it and the water column shows both of them.

Loggers at Hon Rom recorded temperature at 10 and 18 metres from 2008 to 2019, at a station in 19 metres of water at the southern entrance to the bay. Yearly cycles ran between averages of 24°C in winter and 29°C in summer. Extremes reached 31°C, in September of 2010 and 2014, and 21°C between October and March, in 2008 and 2011. Daily swings of up to 8°C tracked the tide.

The structure changes with the season, and that is the part a diver feels. From June to August strong north-northeasterly winds drive upwelling: the surface heats while the deeper water cools, and the column separates. From December to February the pattern reverses into downwelling and mixes, so surface, 10 metres and 18 metres read the same.

Weather splits the year cleanly. The dry season runs January to August and the rainy season September to December, with an average of 1,285 mm falling from September to November, 70 to 80 per cent of the annual total.

That rain arrives through two rivers. The Cai enters north of the city and the Tac, also called the Be, to the south, and both carry sediment into the bay. Their plumes are visible from land and sometimes reach several kilometres offshore. The study that recorded the temperature series attributes the poor development of the nearshore reefs to that sediment together with the 21 to 31 degree annual range.

Tides here are mixed and mainly diurnal, about 40 centimetres at neap and more than 2 metres at spring, which is enough to decide a shallow dive. Our travel wetsuit guide covers the trade-offs at the cold end of that range.

What Typhoon Damrey and the 2021 storms did to the reefs

Typhoon Damrey came ashore in Khanh Hoa at about four in the morning on 4 November 2017, the strongest storm to strike southern Vietnam in 16 years, with maximum sustained winds near 150 km/h at landfall. In this province alone 114,000 homes were damaged or destroyed.

Underwater the accounting is separate and specific. The head of the Nha Trang Bay Management Board put the loss in the richest parts of the bay, Hon Mun, Hon Mot, Hon Tam and the northeast of Hon Tre, at 70 to 80 per cent of corals after Damrey. At Hon Tam alone, hard coral cover fell from 56.8 per cent in July 2017 to 12.5 per cent that December.

Two more blows followed. In 2019 corals began bleaching as water temperatures rose in parts of the bay, and the hard coral bleaching rate that year was 39.5 per cent. At the end of 2021 storms struck the reefs again and up to 70 per cent of the reef in the southwest of Hon Mun and to the south was washed ashore.

The exposure has not gone anywhere. In November 2025 Typhoon Kalmaegi, storm number 13 of the year in Vietnam's numbering, crossed the coast north of the province and brought heavy rain across the stretch from Hue down to Khanh Hoa. Heat is the other threat the board watches: it closed the Hon Chong to Dang Tat reef to visitors from May to August 2026 on advice that coral bleaches if sea temperature passes 30.5°C for two to three consecutive weeks.

The recompression chamber is in Nha Trang itself

Not every dive destination has one within reach. Military Hospital 87, at 78 Tue Tinh in Nha Trang, runs a naval medicine department with hyperbaric oxygen treatment, and diving accidents and decompression sickness are on its list of what it treats.

In September 2018 the department was described as holding one chamber taking six patients at a time, large enough for a doctor to sit inside with them, plus two single-person transparent chambers, staffed by three doctors and four trained technicians and running over 2,500 hyperbaric sessions a year. One case given was a 26-year-old fisherman with diving paralysis who recovered over a month.

The hospital serves the armed forces and the public across the south central provinces, the central highlands, Naval Region 4 and the Truong Sa islands, so the chamber exists for commercial and military divers rather than for tourism. Being near a chamber and being covered for one are different questions, which is what our dive insurance comparison is for.

Khanh Hoa absorbed Ninh Thuan on 1 July 2025 and Nha Trang city ended

Addresses here changed recently, and the change reaches the diving. Under National Assembly Resolution 202/2025/QH15 of 12 June 2025, Ninh Thuan and Khanh Hoa were merged into one province keeping the name Khanh Hoa from 1 July 2025, covering 8,555.86 square kilometres with more than 2.24 million people.

Resolution 1667/NQ-UBTVQH15 of 16 June 2025 then rearranged the units below it: 65 in all, 48 communes, 16 wards and one special zone. Nha Trang city ceased to exist as an administrative unit. Vinh Nguyen ward, which holds the piers the dive boats leave from, was folded together with Van Thanh, Loc Tho, Tan Tien and Phuoc Hoa into a new ward called Nha Trang, 47.13 square kilometres and 136,118 people in 2024.

The merger also pulled a second reef coast into the same province. Vinh Hy bay and Nui Chua, a UNESCO biosphere reserve of 106,646 hectares designated in 2021, with an extensive nearshore coral reef, seagrass and turtle nesting beaches, now sit inside Khanh Hoa in its southern half. If you are choosing a base rather than a dive day, where to learn to dive weighs the same trade-offs across other coasts.