Passage 6.22.7
ἀπέχει δὲ ὡς πεντήκοντα Ὀλυμπίας σταδίους κώμη τε Ἠλείων Ἡράκλεια καὶ πρὸς αὐτῇ Κύθηρος ποταμός· πηγὴ δὲ ἐκδιδοῦσα ἐς τὸν ποταμὸν καὶ νυμφῶν ἐστιν ἱερὸν ἐπὶ τῇ πηγῇ. ὀνόματα δὲ ἰδίᾳ μὲν ἑκάστῃ τῶν νυμφῶν Καλλιφάεια καὶ Συνάλλασις καὶ Πηγαία τε καὶ Ἴασις, ἐν κοινῷ δέ σφισιν ἐπίκλησις Ἰωνίδες. λουομένοις δὲ ἐν τῇ πηγῇ καμάτων τέ ἐστι καὶ ἀλγημάτων παντοίων ἰάματα· καλεῖσθαι δὲ τὰς νύμφας ἀπὸ Ἴωνος λέγουσι τοῦ Γαργηττοῦ, μετοικήσαντος ἐνταῦθα ἐξ Ἀθηνῶν.
About fifty stadia from Olympia is Herakleia, a village of the Eleans, and beside it flows the river Kytheros. There is a spring issuing into the river, and at the spring a sanctuary of the Nymphs. Each one of the Nymphs is individually named, Kalliphaeia, Synallasis, Pegaia, and Iasis, but collectively they are called Ionides. Bathing in the spring provides healing from weariness and all sorts of pains. They say that the Nymphs take their name from Ion, the son of Gargettos, who migrated here from Athens.