Beach
Plage de Boulogne-sur-Mer
France · sea 17.7 °C at its warmest, in August

Sea temperature month by month
8.9Jan
7.9Feb
7.9Mar
9.3Apr
11.4May
13.8Jun
16.1Jul
17.7Aug
17.5Sep
15.7Oct
13.3Nov
10.8Dec
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 Boulogne-sur-Mer?
The sea off Plage de Boulogne-sur-Mer averages 17.7 °C at its warmest, in August, and 7.9 °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 Boulogne-sur-Mer?
The sea here never averages 20 °C in any month, so swimming means cold water all year. Some people do it anyway.
Where is Plage de Boulogne-sur-Mer?
Plage de Boulogne-sur-Mer is on the coast of France, at 50.7325, 1.5940. The map on this site flies straight to it.