Passage 5.7.2
λέγεται δὲ καὶ ἄλλα τοιάδε ἐς τὸν Ἀλφειόν, ὡς ἀνὴρ εἴη θηρευτής, ἐρασθῆναι δὲ αὐτὸν Ἀρεθούσης, κυνηγετεῖν δὲ καὶ ταύτην. καὶ Ἀρέθουσαν μὲν οὐκ ἀρεσκομένην γήμασθαι περαιωθῆναί φασιν ἐς νῆσον τὴν κατὰ Συρακούσας, καλουμένην δὲ Ὀρτυγίαν, καὶ ἐνταῦθα ἐξ ἀνθρώπου γενέσθαι πηγήν· συμβῆναι δὲ ὑπὸ τοῦ ἔρωτος καὶ Ἀλφειῷ τὴν ἀλλαγὴν ἐς τὸν ποταμόν.
Other tales about Alpheios are as follows: they say he was a hunter who fell in love with Arethousa, herself a huntress; but Arethousa, unwilling to marry him, crossed over to the island near Syracuse called Ortygia, and there was transformed from a human into a spring. Through love, Alpheios too experienced the same transformation and became a river.