At my place, that would be called a pond.
That said, a full size hoe will get you real close to that depth. My ponds are somewhere in that neighborhood. (Ford 555C)
That is real deep to be on the edge of if it collapses, nothing good will come of that story.
That said, bigger, deeper, etc. etc. caves, grotto's and bunkers have been dug by hand for thousands of years, so if you have the dedication, and the thought of loosing your life for this hole is acceptable, go for it. For me, it would scare the beejeebus out of me.