There have been many "tests" in that area for sustainable trout resources. Jo Daviess County in particular has had reports of naturally reproducing trout around Apple River. Oddly enough, the waters test the same as their counterparts just across the "infamous" borders. Water temps are similar to other northern streams but summer temps are enough to wipe out the strains of trout.
The Illinois DNR is much less prepared for trout streams than most would like and have only 4 DNR offices. Finances for trout fishing and habitat are few and far between. Our TU group worked out there for a short time and have obtained the water studies for the area. What a shame! Who knows, maybe one day, the masses will travel south for their trout fishing!! LOL