The late JC and me did some basic research with stream thermometers back in the 60's and early 70's on Michigan's AuSable River. We never came to any definitive conclusions based on water temperatures but research does show water temperatures do drive hatches and fish activity. The exact correlation between temperature and trout and hatch activity is also linked to the habitat. In streams where water temperatures are relatively constant, like spring creeks and tail water fisheries, hatches and trout activity are much more difficult to correlate with water temperatures.