Fox river requires no special permit. Not sure where you want to hit. I am in Batavia. Been as far north as ST. Charles dam down to Aurora casino. Several dams in that stretch which require a portage. Plenty of great water.
Get yourself on USGS streamflow data. I use the data from South Elgin as it represents this section. https://waterdata.usgs.gov/il/nwis/uv/? ... 0065,00060
Currently 2520 CFS. That's a healthy flow. I do not wade if its above 2000 CFS. Recent summer floods had it above 10,000 CFS - DO NOT EVEN THINK ABOUT IT! Anything above 3000 and you will be moving way to fast to work an area - blink and you are way down river. The current flow, I consider fishable from a yak, but you only get one cast per spot.
PM me for more info.