I remember seeing this in the theater as a kid and recognizing Dawn Wells from after-school viewings of Gilligan's Island.
I seem to remember she had a PG-rated scene where she bathed in a river. Nude, but not actually revealing. Did I imagine that?
Refriedwhiskey, I think you have confused this film with Grayeagle, which is also a Charles B. Pierce film. In that film, Lana Wood is bathing herself in a stream, is uncovered from the waist up, and suddenly realizes that she is being watched by a one-eyed Shoshone who wants to kill Grayeagle and take her for himself. She screams and covers herself, prompting Grayeagle and the Shoshone to begin fighting.
I saw Winterhawk at the theater, and I own a VHS tape of the film. Dawn Wells never had a bathing scene in WH. The closest to what you describe is when one of the Blackfeet Indians returns from a fight, delivers some news to WH, and falls off his horse into the river due to injuries suffered in the fight. Dawn Wells jumps off her horse, grabs him and holds him up, and yells for someone to help the young Indian. She is fully clothed in the scene, wearing a dress.
Hope this helps!