Listen carefully as I'm pretty sure that was a girl!
I call that feature in the creek a "frost boil" or a place where the water continually flows around a rock throughout the winter giving off water vapour and freezing which can create the fancy hole. I very innocently went into one of them, foot caught in the stirrup, and I ended up in front of the machine with a broken leg. Yes, it is always good to have buddies around and watching your back.