You Can't Step Into the Same River Twice

Heraclitus said that you can't step into the same river twice. This is one of his most famous aphorism, but there are many others he could have used to make an argument. He says it's a different river because of the different waters. So how would that work as an argument, as opposed to just an aphorism? It might be able to reconstruct something that looks much more like an argument if you supposetht we don't have to eliminate any of them.