Time series of water level in major rivers of the Plata basin are examined using altimetry data from the Topex/Poseidon satellite over the period 1993--2001. Ten sites are selected on the Paran¿, three on the Paraguay, one the Uruguay and seven on wetlands. It is confirmed that the seasonal cycle of river levels decreases in amplitude with increasing latitude of the site. The normalized time series for sites along the same river differ mainly by a time-lag corresponding to propagation speeds of about 0.1 ms-1. The interannual variability of the Lower Paran¿, with a strong peak in early 1998 and minima in early 1996 and 2000, shows the remote effects of El Ni¿o/Southern Oscillation (ENSO). The variability of the Upper Paran¿ and Paraguay shows similar ENSO impacts with smaller amplitudes after 1995, and the effects of regional features climate variability before that date (e.g. the South American monsoon). The results support the usefulness of satellite altimetry for a dense and continuous monitoring of river water levels.