ARGYRA was a sea-nymph of the Korinthian (Corinthian) Gulf and also the Naiad-nymph of a spring of the town of Argyra in Akhaia (Achaea) (southern Greece). She was loved by the hero Selemnos who died of grief when she abandoned him and was transformed into a local stream.
Perhaps TRITON though nowhere stated
ARGYRA (Argura), the nymph of a well in Achaia, was in love with a beautiful shepherd-boy, Selemnus, and visited him frequently, but when his youthful beauty vanished, she forsook him. The boy now pined away with grief, and Aphrodite, moved to pity, changed him into the river Selemnus. There was a popular belief in Achaia, that if an unhappy lover bathed in the water of this river, he would forget the grief of his love. (Paus. vii. 23. § 2.)
Source: Dictionary of Greek and Roman Biography and Mythology.
CLASSICAL LITERATURE QUOTES
Pausanias, Description of Greece 7. 23. 1 (trans. Jones) (Greek travelogue C2nd A.D.) :
"The spring Argyra, [of the town Argyra in Akhaia (Achaea)] on the right of the high road, and to the river Selemnos going down to the sea. The local legend about Selemnos (Selemnus) is that he was a handsome lad who used to feed his flocks here. Argyra , they say, was a sea-nymphe (thalassa nymphe), who fell in love with Selemnos and used to come up out of the sea to visit him, sleeping by his side. After no long while Selemnos no longer seemed so handsome, and the Nymphe would not visit him. So Selemnos, deserted by Argyra, died of love, and Aphrodite turned him into a river. This is what the people of Patrai (Patrae) say. As Selemnos continued to love Argyra even when he was turned into water, just as Alpheios (Alpheus) in the legend continued to love Arethousa (Arethusa), Aphrodite bestowed on him a further gift, by blotting out the memory of Argyra."
- Pausanias, Description of Greece - Greek Travelogue C2nd A.D.