Passage 6.22.10
Λετριναῖοι μὲν δὴ Ἀλφειαίαν ἐκάλουν τὴν θεὸν ἐπὶ τοῦ Ἀλφειοῦ τῷ ἐς αὐτὴν ἔρωτι· οἱ δὲ Ἠλεῖοι ---φιλία γάρ σφισιν ὑπῆρχεν ἐξ ἀρχῆς ἐς Λετριναίους ---τὰ παρὰ σφίσιν Ἀρτέμιδι ἐς τιμὴν τῇ Ἐλαφιαίᾳ καθεστηκότα ἐς Λετρίνους τε μετήγαγον καὶ τῇ Ἀρτέμιδι ἐνόμισαν τῇ Ἀλφειαίᾳ δρᾶν, καὶ οὕτω τὴν Ἀλφειαίαν θεὸν Ἐλαφιαίαν ἀνὰ χρόνον ἐξενίκησεν ὀνομασθῆναι.
The people of Letrini indeed called the goddess "Alpheiaia," because of the love Alpheios had for her. As for the Eleans—who had maintained friendship with the Letrinians from the beginning—they transferred to Letrini the rites established among themselves for Artemis Elaphia, and ordained that these rites be observed in honor of Artemis Alpheiaia. Thus, in time, the goddess came to be more commonly known as Elaphiaia rather than Alpheiaia.