Foster Run is a 1.78 mi (2.86 km) long first-order tributary to East Branch Tunungwant Creek.

[2] Foster Run rises about 1.5 miles (2.4 km) northwest of Lewis Run, Pennsylvania, and then flows east-southeast to meet East Branch Tunungwant Creek at Lewis Run.

Foster Run drains 0.88 square miles (2.3 km2) of area, receives about 46.8 in/year (119 cm/year) of precipitation, and is about 85.27% forested.

[3]