A sediment environment of the Gulf of Gdansk is reductive to the iron (III). The iron (II) is a dominant form of this element in the interstitial water, and a total reduction takes place in a sediment layer of up to 20 cm. A speciation of a dissolved iron as well as a total iron concentration is related to types of sediments in a measuring point. It could also be noted that a concentration of each iron form in the above-bottom water layer is much lower than in the interstitial water of the top sediment layer. To illustrate redox conditions in the environment a ratio Fe(III) : Fe(II) was introduced. In the waters, the iron (III) dominates and the Fe(III) : Fe(II) ratio is much higher than the relevant value in the interstitial water.