Beach
Žusterna beach
City Municipality of Koper, Slovenia · sea 25.4 °C at its warmest, in August

Sea temperature month by month
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 Žusterna beach?
The sea off Žusterna beach averages 25.4 °C at its warmest, in August, and 9.6 °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 Žusterna beach?
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 Žusterna beach?
Žusterna beach is on the coast of City Municipality of Koper, Slovenia, at 45.5466, 13.7097. The map on this site flies straight to it.