Ancient romans (from late Republic to the III century crisis, at least) were big fan of water and the sea.

We know from their musive art and from Lucullus they liked seafood to the point of obsession, and the fishing industry was florent and rich.

At the same time one common turn of phrase to signify ignorance was: "They can't read nor swim". Many thermae had plunging and swimming pools, and we have plenty of mosaics depicting swimmers, both in rivers and in the sea (we actually have those since Etruscan times, like in the "Diver tomb". It goes way back).

So: Romans were a Mediterranean culture, and like all Mediterranean cultures, they were really fond of the sea.

During the "Imperial Golden age" of the I and II century we see, through archaeological findings, a flourish of seafront proprieties: large villas and domus built on the coast of Latium, Campania and Tuscany, and on the islands.

These were roman villas, so not actually just "resorts", but small villages owned by a rich individuals, usually of patrician or equestrian class, inhabited by their workforce, servile or otherwise.

In those waterfront villas we found different kinds of abitative and working spaces, fulfilling different purpouses: they both had productive and recreative/domestic function.

We can assume they worked like country villas: they were production centres, semi-industrial fishing hubs, channeling the precious seafood to Rome through the waterways, and as recreative and entertainment resort for the owner, his family and his guests.

So... the Roman loved to swim and built luxury villas on the waterfront.

Romans weren't obsessed by white skin, and considered a brownish color to be the mark of the civilized (aka, Mediterranean) people, but we know, from archeological findings and primary sources (mostly Ovid) that their makup was aimed to oil and fatten the skin: they didn't mind for than, but were obsessed by smooth skin. Smooth skin and sun baths don't mingle well.

We also know from art that Romans praticed sport naked or semi-naked, including women: they didn't need protection from the sun. And seaside cities like Capua or Naples still had plenty of baths that included swimming pools.

So... they loved their sea, they loved to spend time on the seafront, they loved to swim and they certainly did in the sea, but you shouldn't expect long sportive swimming in the sea or long lazy afternoons sun tanning on the Tyrrenian beaches: the sea was for relaxation on the frescoed porch, looking at the waves from the confortable shade of your villa, the bath and the termae wer for sport and fun.