Spring Run (also known as The Gut) is a tributary of the West Branch Susquehanna River in Northumberland County, Pennsylvania, in the United States.

The stream then turns west for a few tenths of a mile, reentering Delaware Township and crossing Pennsylvania Route 405.

In then turns south-southwest for a short distance, reentering Watsontown and reaching its confluence with the West Branch Susquehanna River.

[1] Spring Run joins the West Branch Susquehanna River 16.54 miles (26.62 km) upstream of its mouth.

[2] In the early 1970s, approximately 71 acres (29 ha), or 8.56 percent of the watershed of Spring Run, was residential land.

[6] Moran Industries once applied for a permit to discharge stormwater into the stream during construction activities.