Ph.D. (Zoology) / The present study deals with the effects of metal-polluted aquatic habitats at five different localities on the Witwatersrand and the Orange Free State on the concentrations of lead, nickel, copper and cadmium in the organs and tissues of the Redknobbed Coot, Fulica cristata, the Sacred Ibis, Threskiornis aethiopicus, and the Reed Cormorant, Phalacrocorax africanus. The physical and chemical conditions of the water and the sediments which prevailed during the period of survey at the various sampling sites suggest that concentrations of parameters such as phosphates, nickel and lead in a number of cases exceeded the limits laid down by Kempster et at. (1980) for acceptable river water quality standards in South Africa. The major sources of pollution responsible for these conditions can primarily be related to sewage, mine and industrial effluents (urban) as well as agricultural practices (rural), respectively. Mining activities were largely responsible for the acidification and miniralization as well as metal pollution of the water and sediments, especially so at the Marievale Bird Sanctuary in the Blesbokspruit catchment area. However, automobiles are suspected to contribute much towards the lead concentrations in the water and sediments at all the sampling sites. Levels of cadmium were generally low and may be the only one of the four metals analysed which truly reflected unpolluted, environmental conditions for this metal in the water and sediments of all the sampling sites. The nutrient loads which suggest mild to moderate eutrophication of the water at all the localities can largely be attributed to sewage effiuents and surface runoff waters from the surrounding townships on the Witwatersrand as well as from inorganic fertilizers from farm lands in the vicinity of the Steynsrus and Senekal farm dams in the Orange Free State. These conditions resulted in the overall increase in primary and secondary production of the affected waters which also coincided with the development of submerged and floating water weeds such as Potamogeton pectinatus and Azolla filiculoides, respectively. The herbivorous Redknobbed Coot and to a lesser extent the piscivorous Reed Cormorant, benefitted directly or indirectly from these conditions. Data obtained during the investigation present a complex situation in terms of the environment and the biological availability of the four metals under discussion. A number of factors in both the abiotic and biotic components may have had an effect on fluctuations in metal concentrations. These may have acted individually and/or synergistically, making the interpretation of the data difficult. Cadmium occurred in the lowest concentrations of all four metals in all four the organs and tissues during all four seasons of investigation. In the case of the rest of the metals as well as the organs and tissues no specific, clear seasonal trend or sequence in the concentrations of the metals was discernible. Copper in the kidney and liver and lead in the bone and blood tissues had the highest mean concentrations over the four seasons of investigation. As far as the winter and summer seasonal tendencies are concerned, statistically significant differences occurred in the concentrations of some metals in specific organs and tissues between the winter and summer seasons, respectively. However, values recorded were not necessarily higher during a particular season. Lead (liver) and cadmium (kidney) concentrations were found to be significantly higher in winter 1991 whilst cadmium and copper (both in the blood) were significantly lower during this same season, compared to winter 1992. Concentrations of nickel did not differ significantly between organs and tissues such as the liver and blood for particular seasons. It was only nickel in the kidney and cadmium in the bone tissue which reflected definite seasonal trends for the four successive seasons of investigation.