The Swanfleet or Nîn-in-Eilph was a marshy area in eastern Eriador through which the lower reaches of the Glanduin (or "Swanfleet river") flowed before it joined the Mitheithel (Hoarwell). The Swanfleet was effectively an inland delta, with uncertain streams and a very uncertain difference between land and water.
It strongly resembled the Gladden Fields on the other side of Hithaeglir, and as such many Stoors felt right at home here after their migration into Eriador. These Stoors remained here until the Great Plague nearly wiped them out, and the remainder then went to the Southfarthing of the Shire.
At the east end of the Swanfleet was a waterfall, beyond which was a ford over the Glanduin, from where led a road to the ruins of Ost-in-Edhil, the ruined city of Eregion.