  Of these only the first has the linguistic density characteristic of Heraclitus’ words. The second starts out with the same three words as B12, but in Attic, not in Heraclitus’ Ionic dialect, and the second clause has no grammatical connection to the first. The third is patently a paraphrase by an author famous for quoting from memory rather than from books. Even it starts out in Greek with the word ‘river,’ but in the singular.  There is no evidence that repetitions of phrases with variations are part of Heraclitus’ style (as they are of Empedocles’). To start with the word ‘river(s)’ goes against normal Greek prose style, and on the plausible assumption that all sources are trying to imitate Heraclitus, who does not repeat himself, we would be led to choose B12 as the one and only river fragment, the only actual quotation from Heraclitus’ book.  This is the conclusion of  Kirk (1954) and  Marcovich (1967), based on an interpretation that goes back to  Reinhardt (1916). That B12 is genuine is suggested by the features it shares with Heraclitean fragments: syntactic ambiguity (toisin autoisin ‘the same’ [in the dative] can be construed either with ‘rivers’ [“the same rivers”] or with ‘those stepping in’ [“the same people”], with what comes before or after), chiasmus, sound-painting (the first phrase creates the sound of rushing water with its diphthongs and sibilants), rhyme and  alliteration.[2]