Aquatic sediments are important sinks of inorganic and organic pollutants as well as of nutrients in highly industrialized and densely populated areas. As many aquatic organisms live in or on the sediments, polluted sediments provide a pathway for the chemicals to food-chain organisms, and finally to man. Sediment-water interactions play a fundamental role in biogeochemical cycling of the elements. One of the most important reactions is the mineralization of organic matter during early diagenesis, which not only leads to anoxic conditions connected with a recycling of nitrate, phosphate, and ammonia but changes the chemical bonding of heavy metals into more soluble species. Our study carried out on freshwater sediments enabled us to show whether heavy metals and nutrients are released into the overlying water under changes in physicochemical conditions. The information is important to water management and sediment dredging activities in harbour areas.