"Fonte Aretusa - This is the legendary cradle of the city [Siracusa]. The nymph Arethusa, pursued by the river-god Alpheus, took refuge on the Island of Ortygia where she was changed into a spring (fonte) by Artemis. Though near the sea, the fountain, built into a wall, runs with fresh water."
The blurb above fails to mention that the wood-nymph Arethusa began her swim in Greece and reappeared in Sicily. Alpheus took on his river form in order to join her and so for thousands of years the people of Ortygia have held the Alpheus River in Greece to be the source of their freshwater fountain.
Alpheum fama est huc Elidis amnem, occultas egisse vias subter mare; qui nuncore, Arethusa, tuo Siculis confunditur undis.
Alpheus, as old fame reports, has found from Greece a secret passage under ground, by love to beauteous Arethusa led; and, mingling here, they roll in the same sacred bed.
Virgil - Aeneid (III, 692-95)
Translated by John Dryden
The temple to Apollo on Ortygia.