Beach
Agathopes
Syros-Ermoupoli Municipality, Greece · sea 24.3 °C at its warmest, in August

Sea temperature month by month
Monthly means in °C, NOAA OISST v2.1 climatology 1991–2020.
About
tourist beach in Syros, Greece
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 Agathopes?
The sea off Agathopes averages 24.3 °C at its warmest, in August, and 15.4 °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 Agathopes?
The sea reaches 20 °C or more from June to October. Twenty degrees is where most swimmers stop calling water cold; below it, a wetsuit helps.
Where is Agathopes?
Agathopes is on the coast of Syros-Ermoupoli Municipality, Greece, at 37.3857, 24.8807. The map on this site flies straight to it.