More specifically this was in the SW corner of Salmon Arm Bay near the mouth of the Salmon River. This requires parking at Peter Jannink Park then trudging out across wet mud for several hundred meters. The bird is presumed to have continued south but if you can find some big pipit flocks you may get lucky. Morning is by far the best time for peak numbers.
There are 9 other records of White/Black-backed Wagtail for BC, but this is the first occurrence of one in the interior.