Lycaon’s body is cast into Scamander for its eddies to carry downstream.
See evidence text
“Then Achilles caught him by the foot and flung him into the river to go down stream, vaunting over him the while, and saying, ‘Lie there among the fishes, who will lick the blood from your wound and gloat over it; your mother shall not lay you on any bier to mourn you, but the eddies of Scamander shall bear you into the broad bosom of the sea.”