Over the last century the discharge of crude or partially treated sewage has probably been the most widespread, most documented and certainly the best understood form of pollution entering the aquatic environment. In the past two decades, however, there has been an increasing public aware­ ness of the potential hazards that exist from the contamination of the freshwater environment by toxic substances associated with the mining industry. World demand for minerals has intensified the exploitation of natural resources. In most western and newly developed countries significant mining proposals are now strenuously regulated to protect the environment. These involve economic and legislative measures and the use of appropriate control technologies. This concern will undoubtedly continue to spread worldwide requiring a programme of enlightened environmental protection management policies and practices for the future. This book has been prepared as a synthesis of our current understanding of the effects of various heavy metals and acidic discharges likely to contaminate the freshwater environment as a direct result of mining activities. The review is based upon the dissertations of former BP spon­ sored students who were engaged to provide a better scientific understanding of the causes of environmental problems associated with this industry. It gives us great pleasure to publish this information for use and appli­ cation by a wider audience as part of the contribution of The British Petroleum Company p.1.c. to European Year of the Environment.