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264 M. J. JENNINGS, L. S. FORE AND J. R. KARR Large rivers are impounded for three primary reasons: hydropower, navigation and flood control. Flooding in large unregulated rivers generally occurs in predictable, annual cycles to which resident organisms are adapted (Junk et al., 1989). The alteration of large rivers through dam construction disrupts these cycles and dependent ecological processes (Sparks et al., 1990). Dams block the movements of fish, create unnatural flow regimes and alter energy transport between aquatic and terrestrial environments. In addition, the conditions created by reservoirs are well suited to a number of introduced species, resulting in assemblages very different from natural habitats in a region (Gelwick and Matthews, 1990). These disturbances are temporary on an evolutionary time-scale (Noble, 1986) and preclude the expectation of an adaptive community; therefore, terminology such as `reservoir index of biotic integrity' is inappropriate. Here we report on the development of a reservoir fish assemblage index (RFAI) analogous to the IBI, but developed for use in reservoir environments. We have three goals: (1) to define metrics sensitive to the human influence on the biology of reservoirs; (2) to integrate sensitive metrics into a multimetric index for use in the assessment of reservoir condition; and (3) to provide an analysis structure that will give timely information useful to citizens and policy-makers. We evaluate the statistical properties of the data set and the index and discuss the potential and limitations of this approach to reservoir biomonitoring. The Tennessee River The Tennessee Valley Authority (TVA) maintains reservoirs on the Tennessee River and its major tributaries (Voigtlander and Poppe, 1989). The mainstem consists of nine impoundments, starting down- stream with Kentucky Lake, located near the confluence of the Tennessee and Ohio rivers, and ending upstream with Fort Loudoun, where the Holston and French Broad rivers join to form the Tennessee. Tributary reservoirs located at higher elevations function as storage for flood control and for power generation. The Tennessee River system is subject to point source and non-point source pollution, habitat modification, N CZ U N NE? PTOL TAXA Reservoir Quality Figure 1. Predicted relationship of selected metrics to reservoir quality (modified from Karr, 1993). Each metric is expected to display a unique pattern of sensitivity along the gradient of human influence or reservoir condition. Metrics shown: TAXA, total number of fish species; TINT, number of intolerant fish species; PTOL, proportion of individuals as tolerant species; PINV, proportion of individuals as invertivores; and PDIS, proportion of individuals with diseases, parasites or anomalies poor good