Coal Run (North Branch Buffalo Creek tributary)
Coal Run begins near a valley in Lewis Township. It flows southeast for several tenths of a mile before entering West Buffalo Township. Immediately upon entering that township, the stream turns east-southeast for several tenths of a mile, receiving one unnamed tributary from the left. It then flows east for a few miles, receiving three more unnamed tributaries from the left. After a while, it turns east-southeast for a few tenths of a mile before turning east again and receiving another unnamed tributary from the left. The stream then flows east-northeast for several tenths of a mile until it reaches its confluence with North Branch Buffalo Creek. Coal Run joins North Branch Buffalo Creek upstream of its mouth. Coal Run has no named tributaries. However, it has a number of unnamed tributaries. The stream codes of these unnamed tributaries include 19039, 19041, and 19042. Various tributaries to Coal Run are designated as impaired waterbodies. The cause of the impairment is nutrients and siltation, while the source is grazing-related agriculture. The total maximum daily load date is 2015. Streams in its watershed are also impacted by E. coli and thermal radiation. The stream and a number of others in Union County have been described as "not as clean as they should be".
In 2000, the load of sediment in Coal Run was and in 2008, it was . This equates to between per year. However, in the future, it could be reduced by 61.76 percent to per year. In 2000, row crops and streambank erosion were the largest contributors of sediment, contributing , respectively. A total of came from hay and pastures, came from unpaved roads, came from low-density urban land, and came from other sources. The nitrogen load of Coal Run in 2000 was , while in 2008, it was . This corresponds to between . In the future, the annual nitrogen load could be reduced by as much as 20.57 percent to . In 2000, the phosphorus load of Coal Run was , while in 2008, it was . This equates to slightly less than per year. However, in the future, the phosphorus load could be reduced by 43.82 percent to per year. The elevation near the mouth of Coal Run is above sea level. The elevation of the stream's source is between above sea level. There is no fencing or streambank stabilization in the watershed of Coal Run. The watershed of Coal Run has an area of . The stream is entirely within the United States Geological Survey quadrangle of Mifflinburg. The watershed of the stream makes up 3 percent of the Buffalo Creek drainage basin. There are of streams in the watershed, including in agricultural land. Agricultural land makes up 50 percent of the watershed of Coal Run and forested land makes up 40 percent. Impervious surface make up 3 percent of the watershed, though this could rise to 24 percent in the future. There are of no-till conversions in the watershed. The agricultural land in the watershed of Coal Run includes of row crops and of hay and pastures. A total of of agricultural land are on slopes of more than 3 percent. Coal Run was entered into the Geographic Names Information System on August 2, 1979. Its identifier in the Geographic Names Information System is 1172067. A steel arch bridge carrying T-394 over Coal Run was built in 1984. It is long and is located north of Mifflinburg. Wild trout naturally reproduce in Coal Run from its headwaters downstream to its mouth. Vegetated buffer strips occur along of streams in the watershed of Coal Run.
The pathogen load of Coal Run is 7.058 × 1015 organisms per month, though this could be reduced to 6.686 × 1015 organisms per month in the future. The largest contributors of pathogens are urban areas and farm animals (6.526 × 1015 and 5.503 × 1014 organisms per month, respectively). Septic systems and wildlife contribute 1.054 × 1012 and 4.451 × 1011 organisms per month, respectively.
Watershed
The watershed of the stream has an area of . The watershed mostly consists of agricultural and forested land.