The river Nymphaios flowed into the Black Sea near the Greek colony of Herakleia (Heraclea) on the border of Bithynia and Paphlagonia. It was probably the River Billaeus (historical name). The major neighbouring rivers were the Parthenios to the east and Saggarios (Sangarius) to the west.
Presumably THE NYMPHAI NYMPHAIIDES
CLASSICAL LITERATURE QUOTES
Quintus Smyrnaeus, Fall of Troy 6. 470 ff (trans. Way) (Greek epic C4th A.D.) :
"Nymphaios' (Nymphaeus') stream, hard by a cave, a wide and wondrous cave : sacred it is men say, unto the Nymphai (Nymphs), even all that haunt the long-ridged Paphlagonian hills, and all that by full-clustered Herakleia (Heraclea) dwell."
- Quintus Smyrnaeus, Fall of Troy - Greek Epic C4th A.D.