The USGS gauge on the Oswegatchie in Harrisville provides an "approximation". The benchmarks below have many variables, so make sure you assess each drop yours
This is the final large drop. The river again splits with a large amount of water flowing right. The right side becomes difficult to run at high water, for this side scout right. The left channel has nice 7 foot waterfall, scouting for this is best left, as well as portaging. The rock on the river next to the falls (seen in picture) is a sive, this can be seen especially at low water.