The sea around Ibiza is at its coldest in February at roughly 14 degrees and at its warmest in August at about 26. It lags the air by about two months, which means October swimming is warmer than June swimming and surprises people booking a late holiday.
The figures below are satellite sea-surface averages. Any given week can sit a degree or two either side.
The year in numbers
What those numbers feel like
Above 24 degrees, from July to September, the water is warm enough that nobody hesitates at the edge.
Between 20 and 24, in June and October and into November, it is comfortable for a swim and cool on the way in. This is the range most northern Europeans would call pleasant.
Between 16 and 20, April, May and December, is swimmable for a determined few and short.
Below 16, January to March, wants a wetsuit. The water is at its clearest then, which is why the divers keep going.
Why October beats June
The sea takes the whole summer to warm and the whole winter to cool, so it peaks two months after the air does. June air is warmer than October air, and October water is warmer than June water by a degree or so. For a swimming holiday rather than a sunbathing one, the back end of the season is the better booking.
Where it varies
Sheltered shallow bays on the east coast, such as Cala Llonga, warm faster than the deep water off the south-west. A few days of northerly wind can pull cold water up and drop the temperature noticeably in a bay that was warm the week before.
Quick answers
When is the sea warmest on Ibiza? August, at about 26 degrees.
When is it coldest? February, at about 14.
Can you swim in October? Yes. The water is around 23 degrees.
Can you swim at Easter? It is about 16 degrees. Brief, and better with a wetsuit.
Is the water warmer in June or October? October, by a degree or so.
Do I need a wetsuit in winter? For anything beyond a dip, yes.