The transport (advection and dispersion) of a slug of soluble or suspendable material in a river is analyzed by two mathematical descriptions. The models are compared and are applied to a dye study on a 10.7-mile (17.2-km) long reach of the Upper Mississippi River upstream from pool no.2. One model is a mixed cells-in-series (CIS) model and the other is an advection-dispersion (AD) model. Bulk parameters used in both models are related to each other and three sets of field data. The CIS model is simpler in formulation and application than the AD model. Both models give very similar results for the field study. Both models show good agreement for nearly symmetrical time-concentration distribution, but give only a fair description of skewed time-concentration curves. An explanation is provided.