My three years hates bathes all I have to say is are you ready for a bath she startes to cry.

Try using some rubber toys that float like rubber duckies or plastic fishies and add some gentle baby's bubble bath.

Is there some negative association with water or bathing that she may have?

I would agree with all that Kit said but just to be sure I would sit down with her when you have no intention of bathing her, maybe while you are in a park or some other area that insists bathing not be an option and ask her why she doesn't like it.

By the by, does she enjoy swimming or any other water related activities?

I suggest,you both bath a few teddys and dolls together,go through the same motions as you would with her,if she does not want to wash the dolls hair,that could be the problem,for example,she saiys,dolly doesn't like her hair washed cause the water gets into her eyes... with play and some gently questions you can get to the bottom of it.

Also you could try a shower attachment to the bath,she can have some control over the water.

Check out bathing songs for children,Making Bath Time Fun For Kids With Tactile Defensiveness (http://www.sensory-processing-disorder.com/bath-time-fun.html)...

Although the link posted states sensory processing disorder,the songs and tips included prove popular with all children and may give you some ideas.