Recent advances in time series analysis provide alternative models for river flows in which the innovations have heavy tails, so that some of the moments do not exist. The probability of large fluctuations is much larger than for standard models. We survey some recent theoretical developments for heavy tail time series models and illustrate their practical application to river flow data from the Salt River near Roosevelt, Arizona. We also include some simple diagnostics that the practitioner can use to identify when the methods of this paper may be useful. ¿ 1998 American Geophysical Union