Beach
Blue Lagoon
Manggis, Indonesia · sea 28.9 °C at its warmest, in April

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.
About
beach in East Bali, Indonesia
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 Blue Lagoon?
The sea off Blue Lagoon averages 28.9 °C at its warmest, in April, and 26.7 °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 Blue Lagoon?
The sea reaches 20 °C or more from All year. Twenty degrees is where most swimmers stop calling water cold; below it, a wetsuit helps.
Where is Blue Lagoon?
Blue Lagoon is on the coast of Manggis, Indonesia, at -8.5300, 115.5132. The map on this site flies straight to it.