Beach
Plage Richelieu Ouest (zone de baignade)
Agde, France · sea 22 °C at its warmest, in August

Sea temperature month by month
Monthly means in °C, NOAA OISST v2.1 climatology 1991–2020, sampled 16 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 Plage Richelieu Ouest (zone de baignade)?
The sea off Plage Richelieu Ouest (zone de baignade) averages 22 °C at its warmest, in August, and 11.8 °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 Richelieu Ouest (zone de baignade)?
The sea reaches 20 °C or more from July to September. Twenty degrees is where most swimmers stop calling water cold; below it, a wetsuit helps.
Where is Plage Richelieu Ouest (zone de baignade)?
Plage Richelieu Ouest (zone de baignade) is on the coast of Agde, France, at 43.2749, 3.4916. The map on this site flies straight to it.