Adjust fly-fishing tactics to catch more trout as summer fades to fall

Fly-fishermen know that their summer outings are often limited to certain streams and stream sections that remain cold enough to host trout throughout even the hottest of weather. 
Some of these are the well-known limestone spring creeks of southern Pennsylvania, such as the renowned LeTort Spring Run and Falling Spring Branch. Tactics on these waters include nymph fishing for trout, dry-fly fishing with terrestrial insect imitations, and fishing to hatches of tricorythodes mayflies where they can still be found.