Beach
Portstewart Strand
United Kingdom · sea 14.1 °C at its warmest, in September

Sea temperature month by month
Monthly means in °C, NOAA OISST v2.1 climatology 1991–2020, sampled 24 km offshore, at the nearest open water cell of a 0.25° grid.
About
Portstewart Strand is a sandy, two-mile long beach in Portstewart, County Londonderry, Northern Ireland, on the northern Atlantic Ocean coast of the island of Ireland.
Questions
How warm is the sea at Portstewart Strand?
The sea off Portstewart Strand averages 14.1 °C at its warmest, in September, and 7.8 °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 Portstewart Strand?
The sea here never averages 20 °C in any month, so swimming means cold water all year. Some people do it anyway.
Where is Portstewart Strand?
Portstewart Strand is on the coast of United Kingdom, at 55.1680, -6.7450. The map on this site flies straight to it.