The reported investigation was undertaken to determine the effects of coal humic acid leached from coal under coal slurry pipeline conditions and related circumstances upon the growth of algae and upon potential eutrophication of waters exposed to coal humic substances. Coal humic acid was prepared by the partial oxidation of Wyoming subbituminous coal with hydrogen peroxide in a basic medium. At lower levels the product was found to stimulate the growth ofChlorella vulgarisalgae. Optimum growth was obtained at 75 mg/liter of coal humic acid for algae acclimated to coal humic acid and 55 mg/liter for non‐acclimated algae.