This data release includes estimates of annual and daily concentrations and fluxes for nitrate plus nitrite, total phosphorus, and suspended sediment for two sites in the Upper Macoupin Creek Basin watershed (UMCB) produced using the Weighted Regressions on Time, Discharge, and Season -- Kalman Filter (WRTDS-K; Zhang and Hirsch, 2019) model in the Exploration of and Graphics for RivEr Trends (EGRET) package (Hirsch and De Cicco, 2015). It also includes a model archive (R scripts in Scripts.zip) used to retrieve and format the model input data and run the model. Input data, for Macoupin Creek at Highway 111 near Summerville, Illinois, and Macoupin Creek at Highway 108 near Carlinville, Illinois (U.S. Geological Survey site numbers 05586745 and 05586647, respectively), including discrete concentrations and daily mean streamflow, were retrieved from the National Water Information System database (USGS, 2021). Annual and daily estimates range from water year 2018 through water year 2021 (although water year 2018 is protracted due to data collection starting on October 24, 2017). Reference: Hirsch, R.M., and De Cicco, L.A., 2015, User guide to Exploration and Graphics for RivEr Trends (EGRET) and dataRetrieval: R packages for hydrologic data (version 2.0, February 2015): U.S. Geological Survey Techniques and Methods book 4, chap. A10, 93 p., https://dx.doi.org/10.3133/tm4A10. U.S. Geological Survey, 2021, USGS water data for the Nation: U.S. Geological Survey National Water Information System database, accessed 12/15/2021, at https://doi.org/10.5066/F7P55KJN Zhang, Q., and Hirsch, R.M., 2019. River water‐quality concentration and flux estimation can be improved by accounting for serial correlation through an autoregressive model: Water Resources Research, v. 5, no. 11, p. 9705–9723, https://doi.org/10.1029/2019WR25338.