Corrosion of copper, 68 brass, aluminum alloy D16 and steel St3 has been analyzed in natural fresh waters. The date obtained are indicative that the corrosion rates of copper and alloys of nonferrous metals in natural river waters at the initial stage of corrosion process are essentially reduced while subsequently their corrosion rates tend to increase which the authors associate with the destruction of protective film on their surface. Steel in 5 river waters examined also corrodes with high rates; however, in 72 hours its rates get stabilized and tend no toward rise.