I read this great article about where to vacation in Korea during the summer months when it gets extremely hot and came across this beautiful sandy beachy place called Hwanjinpo. It islocated near the East Sea. The water is supposed to be a gorgeous blue and the beaches are pristine. Sounds like my kind of place.
The waters here are shallow and pure, lending themselves to inexperienced swimmers or paddlers. Since a natural bay hems in the beach, there is no danger of strong currents.