Beach
Tanghou Beach
Taiwan · sea 27.5 °C at its warmest, in August

Sea temperature month by month
Monthly means in °C, NOAA OISST v2.1 climatology 1991–2020, sampled 16 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 Tanghou Beach?
The sea off Tanghou Beach averages 27.5 °C at its warmest, in August, and 14.1 °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 Tanghou Beach?
The sea reaches 20 °C or more from May to November. Twenty degrees is where most swimmers stop calling water cold; below it, a wetsuit helps.
Where is Tanghou Beach?
Tanghou Beach is on the coast of Taiwan, at 26.2228, 120.0046. The map on this site flies straight to it.