A case of iron precipitation in glaciofluvial material from Lake Hämeenjärvi near Oulu, northern Finland is described. Special emphasis is placed on the elucidation of the geochemical regime, the Eh-pH conditions and the chemical composition of the groundwater and the precipitate. In the case studied, deposition of iron is a result of a rise of Eh from + 400 mV to + 560 mV at the top of the watertable. On an Eh-pH equilibrium diagram the process, however, operates entirely within the field specified theoretically for ferric hydroxide. The total annual rate of deposition has been calculated to be about 15 g Fe/m2on the basis of an average annual rate of flow of 5 1 water/s in a discharge creek. The texture of the precipitate and the distribution of Fe, Mn, Si and Al in it have been studied using scanning electron microscope and EDS. X-ray diffractometry, TGA and DTA studies show that the precipitate is in an amorphous state and contains 17.90% water expelled below 880°C.