PA DEP classifies it as Cold Water Fishes, managed as Cold Water Fishes — that is the season and creel row to look up. Walnut Creek averages 73.6 °F in July across 1 gauged stretch, so the middle of summer is a morning-and-evening proposition rather than a bad month.
There is no hatch record for Pennsylvania in this dataset, so this page does not guess at one. The season and the water temperature are below.
Pennsylvania publishes no season on this reach in the file this site reads. PA DEP classifies it as Cold Water Fishes, managed as Cold Water Fishes, and that is the row to look up in the digest — the season and creel rules follow the classification rather than the river. What the state designates on this water → Pennsylvania regulations →
July is the warmest month and the one this site measures: 1 gauged stretch average 73.6 °F . Everything either side of July is colder than that.
Walnut Creek — live water temperature, regulations and access