Beach
Moonlight Beach
Victoria, Australia · sea 17.9 °C at its warmest, in February

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.
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 Moonlight Beach?
The sea off Moonlight Beach averages 17.9 °C at its warmest, in February, and 13.6 °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 Moonlight Beach?
The sea here never averages 20 °C in any month, so swimming means cold water all year. Some people do it anyway.
Where is Moonlight Beach?
Moonlight Beach is on the coast of Victoria, Australia, at -38.7486, 143.2050. The map on this site flies straight to it.