How many other words do they need? For you, "no wading" would do it". But what if a kid didn't want to wade, but splash? OK, now we have "no swimming, no wading, no splashing". What about "rinsing off hands"? OK, add that. Oh, "rinsing off feet" after a long day? Sounds nice and refreshing. Add that. Soon enough we have a sign longer than ANYONE is ever going to read, and the whole thing is useless.
I've always gotten the concept that "no swimming" means "we have good reasons to not want you in our water, so stay out". I mean, "we don't swim in your toilet please don't pee in our pool" doesn't specify "don't go #2", but most of us get that we aren't supposed to do THAT, either.