Pollution of the aquatic environment has raised global concern for the environmental persistence, potential toxicity and bioaccumulative nature of trace elements and their associated effects. This chapter discusses related concepts, and sources, transport and distribution of some trace elements considered most hazardous to the aquatic environment (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn). Trace elements from principal anthropogenic sources (e.g., mining, agriculture, industry and municipal wastewater) and significant natural sources (e.g., geological weathering and forest fires) may be transported to water reservoirs by erosion, surface runoff, atmospheric deposition and leaching. Once in the aquatic environment, they interact with abiotic and biotic components of the ecosystem. They are distributed to different compartments of the aquatic ecosystem (water, sediments, suspended particulates and biota) where they undergo various transformations. The transport and distribution of trace elements are governed by hydrodynamic, biogeochemical, organismal and site-specific environmental processes and factors which influence their availability, mobility and toxicity. Global efforts should target at reducing the release of trace elements at source, controlling their transport and removing them from contaminated aquatic environments using promising biotechnological approaches, policing, effective enforcement of regulation, monitoring and research.