Sediment treatment options include dredging, physical and chemical capping, and in situ sediment treatment. In our studies, in situ sediment treatment has been used to oxidize sediment sulphides, control eutrophication and bioremediate organic contaminants. Sediment contamination of various types was studied in 22 sites from six countries in North America, Europe and Asia. In Hong Kong, field testing of sediment treatment oxidized 99% of sulphide and controlled odours. In Lake Biwa, Japan, where excess nutrients in sediments enhanced growth of toxin producing algae, sediment treatment with calcium nitrate blocked growth of these algae. Oxidation of sulphide in Lake Biwa sediments precipitated > 80% of the porewater phosphorus. Oxidation of sulphides and addition of nutrients biodegraded more than half of the organic contaminants in Hamilton Harbour, Canada. The biotreatability of polynuclear aromatic hydrocarbons is very site specific and is faster in sites with higher concentrations of oil.