Arethusa, in Greek mythology, nymph favored by Artemis and loved by the river god Alpheus. While Arethusa was bathing in his stream, Alpheus rose up and tried to abduct her, but she fled under the ocean to the isle of Ortygia. There Artemis changed her into a fountain. But Alpheus followed her and was himself changed into a river and united with her. In ancient times it was believed that the waters of the Alpheus River flowed beneath the sea from Greece and reappeared in the fountain of Arethusa in the harbor of Syracuse.