Seasonal cycles in the concentration and chemical form of transition metal ions in reservoir waters and stratifications of metal concentrations within the depth profiles have been documented. The changes in concentration of iron and manganese through the year with changes in temperature, acidity, and biotic activity are described. Particular attention was paid to time and depth differences in concentrations of certain valence states of manganese and iron by use of electron spin resonance (ESR) absorption and atomic absorption (AA) techniques. The results showed significant differences between the amount of manganese found by the two techniques at any one point. Iron proved to be unsuitable for ESR analysis. Some solid natural mineral deposits from Lake Allatoona in Georgia yielded complex ESR spectra that suggest that they are made up of some ferro-manganese complex.