This data release contains model inputs, outputs, and source code (written in R) for the calculation of daily total phosphorus (TP) concentrations at a sampling site operated by the Klamath Tribes (WR6000), which is located 5 miles downstream of USGS streamgage 11502500, Williamson River below Sprague River near Chiloquin, Oregon. Daily streamflow data from 11502500 were used to calibrate the model along with data provided for the Klamath Tribes for site WR6000. Daily TP concentrations were calculated from 1991-2019 using the USGS Weighted Regression on Time, Discharge, and Season (WRTDS) model. Calibration data are bi-weekly (every two weeks) TP concentrations collected at site WR6000 and analyzed by the Klamath Tribes at the Sprague River Water Quality Laboratory (SRWQL). All concentrations are reported in milligrams per liter (mg/L).