Abstract: The Tioga River and its major tributaries were sampled monthly from September 1973 to May 1975. Water quality in the Tioga River is degraded by acid-mine drainage entering the stream near Blossburg from both strip- and deep-mined areas. The stream supports few species of aquatic life from Blossburg to its confluence with Crooked Creek- Alkaline water of tributaries Mill Creek, Crooked Creek, and the Cowanesque River counteract the acidity carried downstream from Blossburg, and ·the water-quality of the Tioga River gradually improves, supporting a more diversified population of fish and aquatic life. Relationships between selected water-quality parameters have been developed for the sampling stations throughout the basin. Downstream trends were also examined. The relationships will be further refined and implemented in predictive water-quality models as more data are collected.