Hey,
I agree that there's nothing to worry about. Sure, nobody can guarantee that such thing will NEVER happen but the possibility is low, really low. I've been swimming a lot in a lake full of crayfish and nothing bad happened.
Probably it's the same as question - WILL THE PIKE BITE ME IF I SWIM THERE? Probably not but I've heard about 1 (only one!!!) case when starving pike attacked a swimmer though
Don't worry and go on! I'd worry more about survival of your crayfish because you got predators there.
