Beach
Spiaggia del Poetto di Quartu Sant'Elena
Italy · sea 25.6 °C at its warmest, in August

Sea temperature month by month
Monthly means in °C, NOAA OISST v2.1 climatology 1991–2020, sampled 13 km offshore, at the nearest open water cell of a 0.25° grid.
Wikipedia has no article about this beach yet. It is on the atlas from its Wikidata record and its photograph.
Questions
How warm is the sea at Spiaggia del Poetto di Quartu Sant'Elena?
The sea off Spiaggia del Poetto di Quartu Sant'Elena averages 25.6 °C at its warmest, in August, and 13.9 °C at its coolest. These are monthly means from NOAA's OISST v2.1 satellite and buoy record for 1991 to 2020, sampled at the beach's own coordinates.
When can you swim at Spiaggia del Poetto di Quartu Sant'Elena?
The sea reaches 20 °C or more from June to October. Twenty degrees is where most swimmers stop calling water cold; below it, a wetsuit helps.
Where is Spiaggia del Poetto di Quartu Sant'Elena?
Spiaggia del Poetto di Quartu Sant'Elena is on the coast of Italy, at 39.2260, 9.2063. The map on this site flies straight to it.