The Bulgarian Black Sea usually becomes comfortable for swimming early in the summer, reaches roughly 24 to 27°C at its peak and is still about 20 to 21°C as autumn begins. Sudden cold upwelling can drop the water by several degrees overnight, mostly on the northern coast.
Sea temperature by month in the national bulletins
These ranges come from the monthly bulletins of the National Institute of Meteorology and Hydrology (NIMH). Each gives a coast-wide observed range at the start and end of the month. They are readings from two real seasons, not long-term averages, and not Varna or Burgas station means.
| Month | 2025 start | 2025 end | 2026 start | 2026 end |
|---|---|---|---|---|
| May | 13°C | 18°C | 12 to 13°C | 18 to 20°C |
| June | 19°C (Shabla 16°C) | 24°C | 19 to 20°C | 25 to 27°C |
| July | 24°C | 27°C | 25 to 27°C | 23 to 25°C |
| August | 26 to 27°C | 25°C | 24 to 27°C | 24 to 27°C |
| September | 25°C | 21°C | 24 to 26°C | 20 to 21°C |
| October | 20 to 22°C | 18°C south, 15 to 16°C north | not posted | not posted |
The single 2025 figures are approximate.
Reading it as a swimmer
- May: too cold for most people until the final days, at about 18 to 20°C.
- June: the big climb, so mid-June is the usual turning point.
- Late July and August: the peak, mostly 24 to 27°C, with Burgas briefly at 28°C in August 2026.
- September: pleasant early on, then a 4 to 5°C fall in 2026.
- October: a short tail for hardy swimmers.
For crowds and heat rather than water, see the wider timing guide.
Upwelling: why the sea turns cold overnight
Upwelling happens when wind pushes warm surface water away from the shore and colder water from below rises to replace it. The bulletins record it mainly north of Varna, at Cape Shabla and in Varna Bay.
Dated cold snaps
- 14 to 16 May 2025: Cape Shabla fell from 14.0°C to 9.5°C. Overnight on 19 to 20 May, Varna went from 15.1°C to 10.7°C.
- 12 to 13 June 2026: Shabla slid from about 17.5°C to 14.3°C, and Varna from about 22.2°C to 14.5°C.
- 9 to 10 July 2025: Varna Bay fell by up to 16 degrees overnight, then by another 5 to 6 degrees on the night of 17 to 18 July.
On the north coast in May and June, plan on having a warm pool as a backup.
North versus south
The south is often slightly warmer. Most dated upwelling happens north of Varna, and at the end of October 2025 the southern coast was about 18°C, against 15 to 16°C in the north. The south is not exempt, though: Burgas shared a 3 to 4°C drop in late May 2025.
The national tourism portal's summer sea figures broadly support this: Albena 25°C, Golden Sands 24°C and Sunny Day, near Varna, about 24 to 25°C, against 26°C at Sunny Beach. These are headline summer values, not monthly averages. Compare Golden Sands hotels and Sunny Beach hotels, or start with the coast overview.
Lifeguard season and guarded sections
Lifeguard cover is set nationally. The Ordinance on water-rescue activity, adopted by Council of Ministers Decree No. 82 of 3 April 2024, puts lifeguards on bathing beaches every day from 1 June to 30 September, 09:00 to 18:30.
Outside 1 July to 15 September, each beach operator's rescue programme may phase the fully guarded sections, so parts of a long beach may be unguarded in June and late September. Municipal orders with local dates for Varna, Burgas and Nessebar were not found.
Swim near a staffed post, and check the Blue Flag beaches if water quality matters to you.
Too cold to swim? Warm pools by resort area
In May, early June and late September, a warm pool can decide whether you swim at all. The details below come only from each hotel's own website. Where heating or opening months are not stated, ask the hotel. For more off-season options, see hotels that stay open all year.
Kranevo
Therma Palace is open all year: indoor mineral pool 30 to 32°C, outdoor jacuzzi 34 to 35°C, mineral barrels 32 to 34°C. Its outdoor pool is seasonal.
Casa di Fiore heats its indoor and outdoor thermal mineral pools all year, including an outdoor hot pool, but gives no temperatures. Choose it for outdoor winter swimming, and Therma Palace if you want published temperatures.
Sts Constantine and Helena
Ensana Aquahouse has 5 outdoor and 6 indoor mineral-water pools fed by a 46°C hyperthermal source, and its spa runs all year. Its site does not say which pools open in winter or whether they are heated. Compare spa hotels in Sts Constantine and Helena.
Golden Sands
Meliá Grand Hermitage has an indoor pool with mineralised hot water and three outdoor pools, open 08:30 to 18:30. Heating for the outdoor pools is not stated. Its booking calendar showed the hotel opening on 15 May 2026, without saying whether that is annual or when it closes, so confirm before an off-season trip.
Balchik
Lighthouse Golf & Spa Hotel keeps its 20 m by 10 m heated indoor mineral pool at 26 to 28°C all year. The lagoon outdoor pool is heated only in summer. Its site does not say the hotel opens every month.
Pomorie
Grand Hotel Pomorie lists an indoor salt mineral pool at 32 to 34°C and a heated outdoor pool at 29 to 32°C that runs year-round and becomes part of the winter garden in winter. Its larger seasonal outdoor pools are kept at 22 to 26°C. The hotel closes from 20 December 2026 to 15 January 2027. Browse Pomorie hotels.
Burgas
Grand Hotel & SPA Primoretz has an indoor pool in its 3,000 m² 6th Sense spa, and the pool is included in its New Year 2026/2027 package. The site does not say whether the pool is heated, or when its outdoor pool is open.
Nessebar, Sunny Beach and Elenite
Sol Nessebar Palace has a heated indoor pool as well as outdoor pools. Its aquapark runs from early June to the end of September, weather permitting.
In Sunny Beach, Barceló Royal Beach has a heated indoor pool with water up to 25°C, so it is not a warm soak.
In Elenite, Royal Castle Design & SPA does not state on its site whether its pools are heated or open seasonally, so ask the hotel before a cold-month trip.
Questions
Can you swim in the Black Sea in May?
Yes, but expect cold water for most of the month. The bulletins put the coast at about 12 to 13°C at the start of May in both recent years, rising to 18 to 20°C by the end. Mid-May upwelling near Shabla and Varna knocked several more degrees off, so a heated hotel pool is the realistic backup.
Why does the water suddenly turn cold?
The usual cause is upwelling, when colder deep water rises to the surface near the shore. It hit Varna Bay hardest on the night of 9 to 10 July 2025, with a fall of up to 16 degrees, yet the bulletin still recorded about 27°C along the coast by the end of that month.
Is the south coast warmer than the north?
Usually by a degree or two, but not always. The tourism portal gives Sunny Beach 26°C in summer against 24°C at Golden Sands, and the bulletins place most upwelling north of Varna. Southern water still dips: Ahtopol recorded 19.6°C on 13 July 2026, so be ready for cold days on either coast.
Is the sea still warm in October?
Only at the start. In 2025 the bulletin recorded 20 to 22°C on most of the coast as October began, then about 18°C in the south and 15 to 16°C in the north by the end. The October 2026 bulletin had not been posted when checked, and lifeguard cover ends on 30 September.
Are lifeguards on duty in September?
Yes, until 30 September, every day from 09:00 to 18:30 under the national water-rescue ordinance. After 15 September, though, the beach operator's programme may phase the fully guarded sections, so check which stretch is staffed before you swim. By the end of September 2026 the sea had cooled to 20 to 21°C.
