Beach
Plage de la Madrague, Anglet
Anglet, France · sea 22.1 °C at its warmest, in August

Sea temperature month by month
Monthly means in °C, NOAA OISST v2.1 climatology 1991–2020, sampled 15 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 de la Madrague, Anglet?
The sea off Plage de la Madrague, Anglet averages 22.1 °C at its warmest, in August, and 12 °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 Madrague, Anglet?
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 de la Madrague, Anglet?
Plage de la Madrague, Anglet is on the coast of Anglet, France, at 43.5110, -1.5348. The map on this site flies straight to it.