The base habitat in many streams in northern Illinois is basically fine; a cracked, slate limestone (and some sandstone) that is about 8,000 to 11,000 years old (the last glaciers to pass through).
Habitat restoration for such waters usually means taking man-made stuff out of the water (like dams) that restrict seasonal flows, encourage siltation and stifles plant growth and oxygenation.
The killer for planting trout in our flowing waters is temperature. The reason streams are stocked in spring is, that is when the water is 12C (about 53F - max stockable temp). After spring the K3, Fox, Piscasaw, Kish and other smaller streams reach temps of 21C (70F) to 26C (80F) and beyond, with low flow, and O2 levels made worse by algae blooms.
45 to 50F are prime rainbow temps. 70F = death.
Many of those Wisconsin streams are fed by well-oxygenated, multiple cold/cool water springs that hold water temps in check over the summer and winter months. They are also located in areas that do not have the huge amounts of warm, untreated sewage, treated city water, or city and farm rainwater run-off that we do.
My what a difference 50 to 100 miles can make in geography, topography and geology.
Smallmouth are actually an extremely hardy fish to be able to survive the high summer temps (80F+), wide seasonal temp swings (of 35F to 80F+), low O2 levels, algae blooms, and pollution levels. In lakes fish can look for some relief in deeper water and/or near areas holding oxygen giving plant life (not oxygen robbing algae).
Smallmouth have nowhere to go. They simply stick it out and survive (in good numbers, too).
As water quality improves, they manage, usually all on their own (as conditions and the forage base allow), to make their way into more and more waters (small creeks and larger waters like the Des Plaines).
What a wonderful fish. No wonder they are such fighters.