Sometimes you only ever get to places like this one (the Minnehaha Falls in particular) once in your life, and when that "once-in-your-life" happens to be at noon at 101 degrees and a hazy hot and humid sun out, then you have to try and make the best of it. I happen to know - was there on 17 June and it was bright and hot and humid, and I had no tripod at all, nor any filters (as I don't own neither), and tried to take photos of the rushing water myself, too. Had to be handheld... and exposure suffered like it did here, too, I'm afraid. Well, didn't dare to go down to f/36 ... erm: lens doesn't even offer it, and did not try to hold 1/3sec., but... well.
By the way, the eyes don't see the soft, milky, white, rushing waters, the more natural look is the "frozen" one where you see all the ripples, and curls and waves and all...
But in general, of course, those who suggest filters and a proper tripod and all that for waterfall photography, plus a better time of the day, are totally right! And I wholeheartedly agree with all their suggestions. Only sometimes life... ah well, don't we all know...!?!?!