イクシユンケイワヲヘツ

• i to one, to me
• + kosunke lie to someone, deceive someone
• + iwaw sulphur
• + nay stream

Proponent: zenibako_trek（小樽銭函地名歴史研究会） (zenibako_trek (Otaru Zenibako Place-Name and History Society))

The guide's explanation gives the sense directly: these streams all come down from Mt. Iwao, one of them is the main Iwaonai, and one cannot tell which, so the name says the river lies about it again and again. The author reads the name against the Bira group of tributaries, where the parallel courses make the main channel hard to pick out. He takes the name as evidence that the upper Horikappu was called Iwaonai by the Ainu themselves, against the identification of Iwanai with the Unjōya River at the harbour.