Swimsuits Parade, Sydney, Australia

In rivers, lakes, streams and the sea men swam in the nude, where the practice was common. Those who didn't swim in the nude, stripped to their underwear. The English practice of men swimming in the nude was banned in the United Kingdom in 1860. Drawers, or caleçons as they were called, came into use in the 1860s. Even then there were many who protested against them and wanted to remain in the nude. Francis Kilvert described men's bathing suits coming into use in the 1870s as "a pair of very short red and white striped drawers".
Female bathing costumes were derived from those worn at Bath and other spas. It would appear that until the 1670s nude female bathing in the spas was the norm and that after that time women bathed clothed. Celia Fiennes gave a detailed description of the standard ladies' bathing costume in 1687:
The Ladyes go into the bath with Garments made of a fine yellow canvas, which is stiff and made large with great sleeves like a parson’s gown; the water fills it up so that it is borne off that your shape is not seen, it does not cling close as other linning, which Lookes sadly in the poorer sort that go in their own linning. The Gentlemen have drawers and wastcoates of the same sort of canvas, this is the best linning, for the bath water will Change any other yellow.
The Bath Corporation official bathing dress code of 1737 prescribed, for women: