Big Run is a tributary of East Branch Fishing Creek in Sullivan County, Pennsylvania, in the United States.

The stream has a low pH and poor water quality, although that could potentially be remedied.

Both are considered by the Pennsylvania Department of Environmental Protection to be impaired by atmospheric deposition.

Proposed methods of restoring the water quality of Big Run include in-stream limestone sand dosing and road liming.

[3] The elevation near the mouth of Big Run is 1,358 feet (414 m) above sea level.

Most of the rest of the stream is on rock of the Huntley Mountain Formation, but its headwaters are on Burgoon Sandstone.

[3] Big Run and its two unnamed tributaries are designated by the Pennsylvania Department of Environmental Protection for use by aquatic life.

[3] Big Run was listed as by the Pennsylvania Department of Environmental Protection as impaired in 2002.