South of Carlisle, the Letort Spring Run is famous for wild brown trout. It is a spring-fed, limestone creek with a slow, grassy flow about twenty feet wide.
Fly fishing the Letort Spring Run is best known for the 1.5 mile Heritage Trout Angling section south of Bonny Brook Road. This catch-and-release section starts about 300 yards upstream of TR481 heading downstream to the railroad bridge on the south side of Letort Springs Park near Carlisle. Most of the fly fishing on the Letort Spring Run is done from June to September during the prolific trico hatches.