Istria

The sea in Istria peaks in August, when the water averages around 26°C.

The main swimming season runs from June – October, when surface temperatures stay comfortable for extended sessions.

On average, 5 months a year sit above 20°C — the threshold most swimmers describe as pleasant without a wetsuit.

Shoulder months like May and November are noticeably cooler but often quieter, with fewer crowds and steadier weather.

Outside peak season the water drops toward 15°C, so a 3/2mm shorty or full wetsuit makes long swims much more comfortable.

The coldest month is typically February at around 12°C, when cold-water swimmers dominate the coast.

Long-term climatology for Istria shows an annual mean sea temperature of 18°C, ranging from 12°C in winter to 26°C at the summer peak.

The seasonal swing is roughly 14°C between the coldest and warmest month — a useful yardstick when comparing years or checking whether the current sea is running above or below average.

Recent decades have trended slightly warmer at Istria, in line with regional sea-surface temperature records for the wider basin.

Monthly averages below are drawn from multi-decadal climatology and are updated as new observations arrive.