It flows east for a short distance before turning southeast and entering a valley.

Eventually, Sullivan Branch receives the tributary Hunts Run and turns southeast.

Shortly afterwards, it merges with Big Run to form East Branch Fishing Creek.

The averaged acidity and alkalinity at an upstream point, both expressed in units of mg CaCO3 per litre, were found to be 7.23 and 5.03 respectively.

[5] Downstream of the tributary Ore Run, the discharge of Sullivan Branch is 11,177,000 gallons per day.

The aluminum concentration at this point is 0.39 milligrams per liter and the load is 36.50 pounds (16.56 kg) per day.

The acidity concentration is 6.70 milligrams per liter and the daily alkalinity load is 624.92 pounds (283.46 kg).

[5] Downstream of the tributary Pigeon Run, the discharge of Sullivan Branch is 14,693,000 gallons per day.

[5] A total of 5.06 miles (8.14 km) of streams in the watershed of Sullivan Branch are considered to be impaired.

[8] Proposed methods to increase alkalinity in the Sullivan Branch watershed include high flow buffer channels, forest surface liming, in-stream limestone sand dosing, and road liming.

[9] Plants found along Sullivan Branch include red trillium, violets of various colors, and squirrel corn.

[1] The entirety of Sullivan Branch is in Pennsylvania State Game Lands Number 13.