Time series models of reservoir water quality are water resource management tools and provide insight into reservoir dynamics since they account for autocorrelation, seasonality, and trends present in the data. Autoregressive integrated moving average (ARIMA) models were applied to describe patterns in selected water quality variables of Red Rock Lake, Iowa. Models were generated for total phosphorus, total nitrogen, and suspended solids for an 8-year period (1972–1979). Patterns in lake concentration and the usefulness of time series models to lake and reservoir management are described.