Beach
Plage du Solarium
Monaco · sea 24.6 °C at its warmest, in August

Sea temperature month by month
Monthly means in °C, NOAA OISST v2.1 climatology 1991–2020, sampled 13 km offshore, at the nearest open water cell of a 0.25° grid.
About
beach in Monaco
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 du Solarium?
The sea off Plage du Solarium averages 24.6 °C at its warmest, in August, and 13.3 °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 du Solarium?
The sea reaches 20 °C or more from June to September. Twenty degrees is where most swimmers stop calling water cold; below it, a wetsuit helps.
Where is Plage du Solarium?
Plage du Solarium is on the coast of Monaco, at 43.7331, 7.4285. The map on this site flies straight to it.