Beach
Plage de Poulfoën
Plouescat, France · sea 15.4 °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.
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 Poulfoën?
The sea off Plage de Poulfoën averages 15.4 °C at its warmest, in August, and 10.2 °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 Poulfoën?
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 Poulfoën?
Plage de Poulfoën is on the coast of Plouescat, France, at 48.6883, -4.1657. The map on this site flies straight to it.