A study was done on the quality of the waters of the rivers Amargos and Niblinto and their effluents in the Malleco National Park-Chile. The water flows studied are of ritral type, have high slope, low water flow, high speed, low temperature and highly oxygenated waters. Six sampling points were established to perform the physico-chemical characterization. The sampling program, the analytical techniques for preservation and conservation of the samples were set according to the current legal standards. The results show that all the parameters considered are within reference values, concluding that the waters are of good quality.