No, you can't swim in Hyeopjae Beach all year round.
The warmest sea water temperatures in Hyeopjae Beach are found in August when they peak at 28°C (82°F) and lowest in March when they dip to 15°C (59°F).
More info about the annual sea temperatures
The sunniest days in Hyeopjae Beach are in July which has the most hours of sunshine per day with an average of 6.2 hours of sunshine per day, making it quite sunny but with occasional periods of cloudy and overcast skies.
November has the least sunshine with an average of 4.3 hours of sunshine per day, making it quite sunny but with regular periods of cloudy and overcast skies.
An ultraviolet index reading above 11 indicates an extreme risk of harm from unprotected sun exposure. Unprotected skin risks burning in less than 10 minutes. Take all precautions because unprotected skin and eyes can burn in minutes. Tanning will be safest before 10am and after 4pm but only with a good application of sun screen. For those with sensitive skin stay in the shade and wear protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 30+ sunscreen every 2 hours, even on cloudy days. Watch out for relections from water that may increase ultraviolet exposure.