Month-specific sea-surface temperature · Croatia
Mljet Sea Temperature in December
17.1°C
62.8°F
In December, sea-surface temperature near Mljet has a historical monthly average of 17.1°C. This is not the reading for any particular holiday date.
Across 2023–2025, the lowest and highest yearly December monthly means were 16.9–17.2°C. These are not daily extremes.
Previous month
November · 19.4°C
Change into December: -2.3°C
Next month
January · 15.7°C
Change into next month: -1.4°C
Can you swim or snorkel in Mljet in December?
At 17.1°C our temperature-only guide describes the water as cold water. Comfort depends on your cold tolerance, immersion time and wind. A historical average cannot determine whether conditions are safe on any given day.
Do you need a wetsuit?
Use a full 3-5 mm wetsuit and keep the session within your cold-water experience.
Which beach should you choose?
Look for a beach sheltered from the actual forecast waves and wind on your visit. Exposure, currents and entry conditions vary even where water temperatures are similar. Follow local warnings.
Check the current waves, wind and snorkeling forecast →
A live forecast does not predict a future December. Check again close to your trip.
Nearby places in December
Comparable historical averages from independent marine grid cells. Warmer water does not imply safe snorkeling.
Data source and limitations
Source: Open-Meteo Marine API, MeteoFrance sea-surface temperature; 2023–2025. Marine model grid near 42.75, 17.53. Based on 3 yearly monthly means and 2232 recorded samples. Source methodology.
Modelled sea-surface temperatures do not establish underwater visibility, wildlife, calm currents or safe entry.