Rocky shore & cove
Arlo Porth
St. Mary's, United Kingdom · sea 17 °C at its warmest, in August

Sea temperature month by month
Monthly means in °C, NOAA OISST v2.1 climatology 1991–2020.
About
beach in St Mary's, Isles of Scilly, southwest of Cornwall
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 Arlo Porth?
The sea off Arlo Porth averages 17 °C at its warmest, in August, and 9.9 °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 Arlo Porth?
The sea here never averages 20 °C in any month, so swimming means cold water all year. Some people do it anyway.
Where is Arlo Porth?
Arlo Porth is on the coast of St. Mary's, United Kingdom, at 49.9164, -6.3178. The map on this site flies straight to it.