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The objective of the study was to compare the spectra of two reservoirs: a urban reservoir (Santo Anastcio) and a rural reservoir (Ors) and to measure their similarity by means of cluster analyses. Sixteen radiometric measures were carried out in each reservoir, using the FieldSpec3 Hi-Res spectroradiometer. Water samples were taken at 30cm depth, concurrently with spectral measurements, for analytical determination of chlorophyll-a (Chl-a) and total suspended solids (TSS). Electrical conductivity (EC), pH, and Secchi depth transparency (SD), were also measured. Cluster analysis, based in the agglomerative hierarchical method of the spectra resulted in three groups. Group 1 was characterized by high concentrations of Chl-a, ranging from 61.97 to 171.91 g/L. Group 2 by Chl-a, ranging from 14.79 to 57.19 g/L and Group 3 where the opticall active component controlling the water reflectance was the SST with concentration varying between 15.25 to 99.00 mg/L. All spectra from Santo Anastcio (Urban) reservoir were classified in the group1, whereas the spectra from Oros were included in Groups 2 and 3. The results show that the cluster-analysis technique of the water spectra can be used to discriminate water masses of urban reservoirs from those of rural reservoirs provided that their optically active components are different.