Beach
Plage de l'Argentière
La Londe-les-Maures, France · sea 23.5 °C at its warmest, in August

Sea temperature month by month
Monthly means in °C, NOAA OISST v2.1 climatology 1991–2020.
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 Plage de l'Argentière?
The sea off Plage de l'Argentière averages 23.5 °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 Plage de l'Argentière?
The sea reaches 20 °C or more from June to September. Twenty degrees is where most swimmers stop calling water cold; below it, a wetsuit helps.
Where is Plage de l'Argentière?
Plage de l'Argentière is on the coast of La Londe-les-Maures, France, at 43.1214, 6.2612. The map on this site flies straight to it.