The objective of the research is to describe the processes controlling dissolved organic material in the lake water following the 1980 eruption of Mt. St. Helens. The concentrations of DOC (dissolved organic carbon) increased 50-fold after the eruption and these increases influenced the chemistry and biology of the lakes for several years. We have shown that most of this DOC was comprised of organic acids classified as either fulvic or hydrophilic acids, similar to those in typical natural waters. We found that between 1980 and 1983, these organic acid fractions underwent oxidative changes in their chemical characteristics. Similar changes may occur in more typical lakes.