[@Kho] The blood probably bears some of Seihdhara's characteristics, even if it isn't the primary carrier of her essence, so the river would reflect that.

The Giant's Bath is also the location of Hemen, the Gateway to Fengshui Fuyou, not Narzhak's place. It's a big crater lake from which Shengshi is presumably making a bunch of rivers. Shengshi will probably be interested in this new river Seihdhara has made.

The River Seihdhar will likely receive numerous tributaries, which would dilute the blood further downstream.