A four-year study (1972 to 1976) was carried out to determine the long-term changes of organochlorine compound concentrations and of associations of epibenthic fishes and invertebrates in a river-dominated north Florida estuary. We assessed the relative effectiveness of a number of statistical techniques for describing the effects of key physicochemical variables on the estuarine biota. Techniques used included transformations, correlation, regression with dummy variables, two and three-way analysis of variance, multivariate analysis of variance, principal components analysis, factor analysis, canonical correlation, and cluster analysis. Several problems were encountered peculiar to studies of this type: missing observations, the sheer size of the data base in numbers of variables and observations, the domination of other effects by river flow, and extreme and noncyclical variation of some measures over the four-year study period.