Cults Myths and Legends of Ancient Sicily
7.2 Nymphs and river gods: Arethusa
Arethusa was one of the nymphs following Artemis. One day, after a hunt with the goddess, he felt the desire to cool off in the river Alfeo, which flowed in Olympia (in the Peloponnese), between Elide and Arcadia. Here she was seen by the river god Alfeo who fell in love with her, assumed human forms and pursued her in an attempt to possess her. Arethusa asked for help from Artemis who, to save her, transformed it into a spring making it sink into the subsoil and guided it through underground streets making it re-emerge on the island of Ortigia, in Syracuse. Alfeo, however, now determined to satisfy hers, so to speak, insane cravings, he managed to find her, he turned back into a river and crossed the sea to Ortigia in order to mix his waters with hers. This is why, according to this legend, the waters of Arethusa di Sicilia are actually those of the river Alfeo.
Diodorus Siculus speaks of this source, not far from the temple of Artemis, in Syracuse, who says that it was particularly rich in sacred and untouchable fish. The union existing between the river Alfeo in Greece and the Arethusa source of Syracuse, would be explained by the ancient belief according to which, when bulls were sacrificed in the river of Olympia, the waters of Arethusa became numb.. Furthermore, it is said that a cup, won at the Olympic games and thrown into the Alfeo river, would reappear in the Syracusan spring.
It is probable that the legend of Arethusa and Alfeo was imported by some colonists from Elis, who participated in the foundation of Syracuse, and that the good relations that Syracuse had with this Greek region kept the cult of Arethusa alive in the Syracusans.
Indeed, in Olympia, the cult of Artemis was connected to that of Alpheus, having the two divinities in common the same altar. Pausanias (lib VII 24,3) tells that some priests of the temple of Artemis in Egio (in Greece), threw focaccias into the sea saying that they sent them to Arethusa of Sicily.
The famous spring, which has become a symbol of the city of Syracuse, still flows today not far from the church of S. Maria delle Colonne and is a popular destination for tourists.
As evidence of the cult of Arethusa, many coins with his effigy have been found. In a silver decadrachma of Syracuse, dating back to the time of Dionysus I, on one side Victoria is depicted flying on a chariot, on the other the head of Arethusa surrounded by dolphins. The same figure (head of Arethusa with dolphins), an imitation of the Syracusan model, is found in a tetradrachm of Palermo from around 400 BC and in some "Punic-Sicilian" coins from around 350 BC.
Until some time ago there were five hundred lire notes in circulation which carried, imitating it in an almost identical way, the Syracusan silver coin: the head of Arethusa with the dolphins
 Diodorus Siculus lib. V.4
 Strabo VI 2,4.
 Pausanias Lib. VI.22.8
Cults Myths and Legends of Ancient Sicily by Ignazio Caloggero
Alfeo tries to kidnap Arethusa