Transition metal oxides (MnO2, ZnO, CuO) and cations (Mn2+, Fe3+) promoted the polymerization of dissolved catechol (1,2‐dihydroxybenzene) and other catechol and pyrogallol derivatives. The manganese species were the most efficient. Colored polymers were formed from catechol much more rapidly in stream waters than in deionized water buffered to the same pH. Addition of sediments or clays increased polymerization; addition of EDTA or lowering the pH reduced it. Ultrafiltration or autoclaving of the stream water samples had no significant effect. The mechanism appears to incorporate an activation of dissolved O2 to a more reactive species, probably •OH.