The explanations provided certainly sound reasonable. The McKenzie at its exit from the lake is not through mountainous territory but rather through almost totally flat terrain. Could well be that the bottom is subject to all sorts of silt shift and channel alteration.
Once the vessel gets to Hay River and off loads the current cargo then it should be full speed ahead to the mine site.
I guess we all need to focus (self included) that all really good things take time and determination.
Onward and Upward