Swimsuits Parade, Sydney, Australia

In the United Kingdom until the mid-19th century there was no law against nude swimming, with each town being free to make its own laws. For example, the Bath Corporation official bathing dress code of 1737 prescribed, for men:
It is Ordered Established and Decreed by this Corporation that no Male person above the age of ten years shall at any time go into any Bath or Baths within this City by day or by night without a Pair of Drawers and a Waistcoat on their bodies.
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: