For many years, the presence of heavy metals in water and sediments as well as their impacts on both terrestrial and aquatic organisms has been attributed to anthropogenic inputs. In this book, Dr. G.M. Ogendi presents results showing that elevated heavy metals levels may be associated with natural weathering processes and thereby impacting negatively on aquatic and terrestrial organisms. He describes the black shale system with its enriched metal composition, its weathering and impacts on the adjacent aquatic ecosystems. The levels of heavy metals in water, sediments and rock samples were measured in the laboratory. To demonstrate the likely impacts of these heavy metals on organisms, water-flea, fathead minnow, and midge larvae were exposed to the water and sediment samples in whole effluent toxicity bio-assays as described in the USEPA protocols. It was established that the levels of the selected heavy metals in water and sediments in some study sites exceeded the USEPA guideline values. Further, it was found that some metals adversely affected the test organisms. Thus, naturally-derived metals need to be considered in aquatic and terrestrial pollution and impact studies.