Brittany

The sea in Brittany peaks in August, when the water averages around 24°C.

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

On average, 4 months a year sit above 20°C — the threshold most swimmers describe as pleasant without a wetsuit.

Shoulder months like May and October 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 January at around 13°C, when cold-water swimmers dominate the coast.

Long-term climatology for Brittany shows an annual mean sea temperature of 17°C, ranging from 13°C in winter to 24°C at the summer peak.

The seasonal swing is roughly 11°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 Brittany, 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.