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.
More than the internal injuries that could be caused by water forcibly entering the vagina? Probably not.