The anthropogenic contamination of freshwater systems and groundwater by heavy metals from different sources is widespread all over the world. Mined metals and metal ores containing other metals and metalloids as impurities impact the receiving freshwater ecosystems. The mining of black shale areas, and contamination of snowpacks by atmospheric deposition in high mountains contaminate freshwater ecosystems. Mine tailings dams pose a risk of dam failure and the resultant contamination. Contamination can also occur from point sources such as industries and sewage outfalls as well as various diffuse non-point sources like agricultural fields, bare slopes, and others. Heavy metal pollution from non-point sources is especially acute in developing countries. Heavy metals and metalloids in river, lake, and reservoir sediments are bound to the different fractions. Of these, those bound to the exchangeable fraction are the most bioavailable. Metals also vary in their mobility. Disturbances caused by floods, especially flash floods in shallow rivers, bioturbation by benthic organisms, fishing, boating, dredging, sand mining, and similar disturbances could be responsible for the resuspension of sediments and remobilization of metals and metalloids. Groundwater could also be similarly contaminated with heavy metals and metalloids from domestic, agricultural, mining, and industrial sources.