Kit is surprised that people didn’t think she would be able to swim and annoyed at Nat for jumping in after her. 

When Prudence Cruff drops her doll in the water, Kit thinks nothing of jumping in after it.  She knows that the doll is valuable to the child, and she is not aware of how cold the water will be or how people will react.  She feels terribly foolish. 

The others stared at her in suspicion. As though she had sprouted a tail and fins right before their eyes. What was the matter with these people? Not another word was uttered as the men pulled harder on their oars. A solid cloud of disapproval settled over the dripping girl, more chilling than the April breeze. (Ch. 1) 

Embarrassed that Nat jumped in after her, Kit tells him that her grandfather taught her to swim at an early age.  He is baffled, because he had no idea that she could swim.  He is also irritated because he got the only clothes he has wet. 

Kit is annoyed and surprised when Nat tells her that Goodwife Cruff has been telling everyone she is a witch because “no respectable woman could keep afloat in the water like that.”  Kit had no idea that the Puritans usually do not swim in Connecticut’s frigid water, and women never do.  In Barbados, a tropical island, Kit swam all of the time. 

"How dare she!" Kit flared, indignant as much at his tone as at the dread word he uttered so carelessly. "Don't you know about the water trial?" Nat's eyes deliberately taunted her, "'Tis a sure test. I've seen it myself. A true witch will always float. The innocent ones just sink like a stone." (Ch. 1) 

This is Kit’s first introduction to the ways of the Puritans.  She soon learns that restrictions against women swimming are the least of her concerns.  When she lives with her aunt and uncle, there are many more rules and prejudices to keep track of.