Both (El Niño-southern oscillation ENSO)-scale and near-decadal variations in precipitation and river flow have been noted in southeastern South America. Here we focus on the Uruguay river basin and its subcatchments. Both river flow and precipitation are analysed with singular spectrum analysis in an examination of how the signals of the subcatchments are related to the overall basin signal. The approximate 6 year signal and the 3.5 year ENSO signal are the two statistically significant peaks for the river flow. Both signals are present in all the available river flows, but only in the precipitation of the upper two-thirds of the basin. Precipitation in the lower part of the basin shows positive trends. The ENSO signal is strongly modulated at the secular time scale; we construct a simple sinusoidal model for this modulation.