The common term seems to be "water skiing douche" and it is something to protect against. Presumably males and females also need to avoid an anal douche.
Edit: the term is "water skiing enema" for rectally injected water injuries... The worst case scenario is severe lacerations to the vagina wall or a rectal blow out.
Not sure why, maybe males have a protective reflex? For a while women could ride, with warning signs that legs must be crossed at all times. Incidents still happened, so they had to go male only.
