Revere Beach, Boston
Probably wool sleeveless maillot pantaloon. Hat, goggles.
Kellerman wades in the water, balancing herself with her hands. Her feet and ankles are hidden under the water (1).
The Bikini Scientist doesn't possess any original documentation of Kellerman's famous bust, and the secondary (and beyond) sources blur it sometime between 1907 and 1909 and blur the swimming suit as something between her unitard (AK0650) and the maillot pantaloon shown here. The style of costume, with its bare knee, is not out of school for a pinup model of 1907 but it is out of school for the real beach. So the image presented in this position in the story line, and indeed some of the story line, involves conjecture.
This picture of Kellerman posing for an Australian pinup postcard also documents her more revealing costume (AK1E60).
If indeed Kellerman's swimsuit had bare arms and legs it might be similar in contours but thicker than a similar silhouette worn by Ellen Koeniger a decade hence, at Lake George (EK1610).
But even if Kellerman bared her legs in Boston, her more covered unitard will remain one of her signature pieces (e.g., AK0915)
Attributed to Hulton Archive, Getty Pictures. Collected slate.com, 2006. 1 picture.