The Pantanal of Mato Grosso is one of the worldâ€™s largest floodplains (Alho, Lacher et al., 1988), located on the frontiers of Brazil, Bolivia, and Paraguay at approximately 16o to 20o S Latitude and 55o to 58o W Longitude (Fig. 1). Low mountains and plateaus surround the basin, which is approximately 140,000 km2 in area. The climate of the Pantanal is tropical and semi-humid, with an annual mean temperature of 25oC. In December the mean temperature is 27.4oC, and in July, the coldest month of the year, the mean temperature is 21.4oC (Garcia, 1984). In the winter, however, the temperature can occasionally drop to nearly 0oC, due to the penetration of cold fronts from the South Pole which advance through the valleys of the ParanÃ¡-Paraguay river systems (Alho, Lacher et al., 1988). More than 50% of the annual rainfall of 1200 mm occurs from December to March. Four hydrological seasons have been defined: 1. Flooding, between October and December; 2. High waters, between January and March; 3. Receding waters (â€˜vazanteâ€™), between April and June; 4. Dry season, between July and September (Por, 1995). During the high waters period, the rivers overflow into a floodplain that drains slowly through the River Paraguay.