I've gone up at the walleye opener, water levels and current were not a problem that year. The poplar/birch trees were leafing up during the trip, starting as bare limbs at first. There was some snow around.
It sounds like it's been higher on other years.

In Sept 2014 I picked up a new Chrismar map.  The ranger said they had added another portage on the north side of the river to help people get past some swift spring water, but it wasn't on the map I bought. She showed me a hand drawn map of it and it was above Poohbah Ck and before some of the older portages. Longer compared to the ones around the rapids, you'd  still need to do those too at the rapids. I think it skips a swift we could paddle when we did it.

Perhaps the park could post a pic of the portage map here, or get some coordinates of the portage.