This is average American beachwear from 1933.

On the left is a cotton 'sunsuit'. Low open back with halter-top tied behind the neck. These were for lounging in the sun, but women would swim in them, too. That may be why they were done in a dark print colors: When wet, the cotton fabric gets like a wet t-shirt: very clingy and would be semi-transparent if it were a solid light color.

Typical swimsuits were summer-weight knit wool (the only "stretch-fabric"). Women's suits have low-cut backs, dark colors (with sometimes bold bands of color). No built-in bras. Suits fit tight around the legs, like bicycle-briefs, but in the early 30s women's suits began to have 'modesty panels' (shown here), so no curvy details would show when the suits were wet. The men's suits show the bicycle-brief legs. Their tops were called 'speed' designs (likely meant to cover male nipples and bellybutton). By 1935, men's trunks with optional tops were sold in Sears catalogs.