Been experimenting with Rainbow Trout in 11 lakes and ponds in central illinois and so far 5 out of the 11 still have thriving trout populations this late into the summer.
4 of the 5 are heavily spring fed, the 5th is where the trout are actually doing the best and it is not spring fed, just elevated, 47 feet deep, windblown, clear, infertile, with a sandy/carbon bottom. The surface temps are in the low 80's and the trout still come up to feed at the surface, even during the middle of the day!
Anyhow, one of the other lakes is 5 acres, 60 feet deep, clear, spring fed, and infertile as well. Those trout have dissappeared since mid-june and I finally got out on the lake to find out where they were hanging out.....We found 'em, the trout are suspended 20-30 feet down and were aggressively hitting rapala ice fishing jigs, curly tailed grubs, and fathead minnows. Surface Temp was 79 degrees, down 20 feet the water temp was 63 degrees, and down 30 feet the temp was 58 degrees. There was still plenty of 02 down that deep! We were even catching a few BG, BC, and LMB down that deep.
Here is a video from fishing today:
Trout Fishing Video
