The Yukon Flats don’t seem to be easy to navigate. Take a look. Not your typical river.
The Yukon constantly erodes and builds its riverbed (it’s more like many beds), the landscape changes each year, so no map, no GPS can be completely reliable. The river flows very slow here. The Book says, if you stop paddling for a while, you will still feel where the main current is steering the kayak. If not, and you happen to select the “wrong way”, you are still making progress, it just takes longer.