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Limnological SamDlinQ At each study location (Island Park, Jensen, and Ouray) one main river and several backwater sites were sampled. The physical-chemical profile was collected using a Hydrolab Corp.l Surveyor II multiparameter probe which measured water temperature (.C), dissolved oxygen (mg/l), pH, specific conductance (~S/cm), and oxidation-reduction potential, used to calculate E7' a measure of the proportion of oxidized to reduced constituents in an aquatic system (Reid and Wood 1976). In the main river, the calibrated multiparameter probe was held about 0.2 m below the water surface, in flowing water, and parameters were recorded after instrument equilibration. In the variously- sized backwaters, the probe was held between 0.1 and 0.3 m below the water surface, and parameters recorded after instrument equilibration. Major ions, nutrients, and heavy metals. - Water samples for analysis of major ions (Na, K, Ca, Mg, HC03, C03, Cl, and S04)' nutrients (total P, ortho-P, N03-N, N02-N, NH3-N, and TKN), and heavy metals (Cd, Cu, Fe, Pb, Mn, In) were collected biweekly in the main river and backwaters. Initially, a one-liter water sample was collected for major ions and kept cold, a 500-ml water sample was collected for nutrients and placed on dry ice, and a 250-mL water sample was collected for heavy metals and preserved with 2.0 mL of concentrated HN03. Midway through the 1987 sampling season, based on initial water sample analyses, we increased the sampling interval of water samples for major ion and heavy metals from biweekly to quarterly. Only samples for nutrient lCertain commercial equipment, instruments, or materials are identified in this paper in order to adequately specify the experimental procedure. Such identification does not imply recommendation or endorsement by the Bureau of Reclamation. 19