A physics problem at sea

First day of the holidays, and the third year in the same place, which is so comfortable in its familiarity. First sea swim of the year too, which immediately posed a problem. You’re swimming along in delicious water and you suddenly hit a cold patch, and it is on the surface. Your feet remain delicious, while your arms shiver inwardly. The people say that there are lots of cold springs around, many of them opening underwater, so that could certainly be it. But as you float there, you try to remember. Cold water is denser than hot water, so it should sink or stay down. But fresh water is less dense than salt water, so it should float or stay up. Clearly, the cold, fresh water is on the surface, so freshness apparently trumps temperature. But is that correct?

Not that it matters. The water is delicious despite, or possibly even because of, the cold patches.