The effect of iron ore tailings on the coastal environment of Ma On Shan, Hong Kong was studied. The iron ore tailings have been dumped along the coast of Tolo Harbour since 1906 from an iron ore mine. Pollutants with a high concentration of various heavy metals together with the effect of land-filling activities recently created conditions detrimental to the already poorly flushed and domestically polluted inland sea in places such as Tolo Harbour. The physical, chemical, and biological parameters of the polluted area were studied. Transects were run downshore and the number of species and the number of individuals were recorded in the field, and edaphic and water analyses were carried out in the laboratory. The animal diversity in the polluted areas varied according to the type of deposited materials and the time of deposition. In general, the number of animals was low compared with the other sites not under the influence of the tailings. Crustaceans and bivalves were the dominant organisms and other organisms were absent in the polluted area, possibly due to the presence of heavy metals and the large amount of fine material deposited. Higher levels of iron, zinc, manganese, and copper were detected in the tissue of the most dominant species, Scopimera intermedia. Copyright © 1978 Published by Elsevier Inc.