Beach
Rena Bianca
Santa Teresa Gallura, Italy · sea 24.9 °C at its warmest, in August

Sea temperature month by month
Monthly means in °C, NOAA OISST v2.1 climatology 1991–2020, sampled 14 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 Rena Bianca?
The sea off Rena Bianca averages 24.9 °C at its warmest, in August, and 13.3 °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 Rena Bianca?
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 Rena Bianca?
Rena Bianca is on the coast of Santa Teresa Gallura, Italy, at 41.2452, 9.1890. The map on this site flies straight to it.