Dark Run is a tributary of Catawissa Creek in Schuylkill County, Pennsylvania, in the United States.

The stream is considered to be a High-Quality Coldwater Fishery and Class D Wild Trout Waters.

Dark Run begins in Union Township, a few tenths of a mile west of the community of Pattersonville.

After some distance, the stream receives two unnamed tributaries and turns north-northeast, cutting through a ridge.

On the other side of the ridge, it receives another unnamed tributary and passes through the southeastern corner of Ringtown before returning to Union Township.

The stream continues north-northeast and receives another unnamed tributary before cutting through another ridge.

[1] Dark Run joins Catawissa Creek 24.83 miles (39.96 km) upstream of its mouth.

[4] The pH of Dark Run 2.66 miles (4.28 km) upstream of its mouth is 7.0 and the concentration of alkalinity at this location is 16 milligrams per liter.

The pH of the stream 1.71 miles (2.75 km) upstream of its mouth is 7.4 and the concentration of alkalinity is 28 milligrams per liter.

The water hardness of the stream 2.66 miles (4.28 km) upstream of its mouth is 34 milligrams per liter.

[4] At 1:35 P.M. on June 19, 1997, the air temperature in the vicinity of Dark Run 2.66 miles (4.28 km) upstream of its mouth was 29 °C (84 °F).

This rock formation consists of siltstone, sandstone, grayish-red shale, and conglomerate.

[4] Dark Run is in the United States Geological Survey quadrangles of Nuremberg and Shenandoah.

[3][4] It is the only tributary of Catawissa Creek to be a High-Quality Coldwater Fishery, but not Class A Wild Trout Waters.