The LeTort Spring Run is a limestone spring creek that flows through Carlisle before joining Conodoguinet Creek. A nature trail follows part of its length, passing through lush riparian vegetation in a pleasant contrast to the town around it. The water is exceptionally clear — you can see the bottom in most conditions — and the watercress and aquatic vegetation of a healthy limestone stream are on display.
The trail is easy walking and popular with birders; the dense streamside vegetation attracts warblers and other species during migration. The LeTort is a catch-and-release fly-fishing-only stream for most of its length, and you may well see anglers working the current for wild brown trout during the cooler months.