yes I tried to fish the Nipigon on foot in late May 2014. found one small spot and quit the river after two days of bushwacking and drove around to terrace bay.
there are quite a few steelhead streams up there between Thunder Bay and Terrace Bay. the further north you go, the later the runs.
Rick Kustich - Great lakes Steelhead book was a great help to me.
the jackpine river was a waste of time , no holding water, too shallow.
the Mackenzie, pine rivers, black sturgeon and wolf are supposed to have good runs.
just googling, I found this :
Gord Ellis Outdoors :: Trout :: Professional Angler, Journalist, Photographer and Broadcaster
I was up there late may, I didn't catch anything apart from a 14" coaster brook trout, but I did see three steelhead caught - two around 7lb, in the 1 1/2 days I fished for steelhead. all were fresh not dropbacks.
if the rivers are blown out, there are literally hundreds of small creeks crossing the highway where you could have a blast for brookies, and may many small and medium size ponds.
In Thunder Bay I stayed at the Valhalla Inn on the way in and out. In Terrace Bay I stayed at The Coach House Motel. Nipigon itself ? - don't bother, its a glorified truck stop.
I had some great Poutine in Drifters restaurant in Terrace Bay.
I hope that helps, its beautiful country up there - the flight into Thunder Bay was something in itself for a right coaster (& former European), with thousands of square miles with no sign at all of humanity - no farms, or roads or lights....or even fields, just pristine untouched land.
best of luck.