Beach
Plage de la Moutte
Saint-Tropez, France · sea 24 °C at its warmest, in August

Sea temperature month by month
Monthly means in °C, NOAA OISST v2.1 climatology 1991–2020, sampled 17 km offshore, at the nearest open water cell of a 0.25° grid.
About
beach in France
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 la Moutte?
The sea off Plage de la Moutte averages 24 °C at its warmest, in August, and 13.2 °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 la Moutte?
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 la Moutte?
Plage de la Moutte is on the coast of Saint-Tropez, France, at 43.2658, 6.6974. The map on this site flies straight to it.