The model is probably Hendrickje Stoffels (about 1625/6 - 1663). She lived in Rembrandt's household from about 1649 until her death. She became his common-law wife and bore him a daughter, Cornelia, who was baptised on 30 October 1654 (the year of this painting).
It has been suggested that the sumptuous red robe on the river bank indicates that the painting might be a sketch for a religious or mythological picture; the model might be in the guise of an Old Testament heroine, such as Susanna or Bathsheba, or the goddess Diana, who were all spied upon by men while bathing. However, there is no evidence for a completed painting after this work and, moreover, Rembrandt did not use oil sketches as preparation for larger-scale paintings.
The handling of the paint is unusually spontaneous. The picture appears unfinished in some parts, for example, in the shadow at the hem of the raised chemise, the right arm and the left shoulder, but it was clearly finished to Rembrandt's satisfaction since he signed and dated it.