Beach
Plage de la Mine d'Or
Pénestin, France · sea 18.2 °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.
About
La plage de la Mine d'Or est une plage publique située sur la commune de Pénestin, dans le département français du Morbihan.
Questions
How warm is the sea at Plage de la Mine d'Or?
The sea off Plage de la Mine d'Or averages 18.2 °C at its warmest, in August, and 9.3 °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 Mine d'Or?
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 la Mine d'Or?
Plage de la Mine d'Or is on the coast of Pénestin, France, at 47.4750, -2.4897. The map on this site flies straight to it.