The transfer of heavy metals from terrestrial sources to aquatic environments significantly disrupts the aquatic ecosystem. This chapter on heavy metals predominantly examines the mechanisms underlying heavy metal mobility and their fate in the entire, including water, sediment and biota of aquatic ecosystems. The primary pathways through which heavy metals are driven from land to water including the natural terrestrial sources predominantly volcanic eruptions, weathering of rocks and soil, forest fires, atmospheric deposition, surface runoff, as well as anthropogenic sources including agricultural runoff, industrial discharges, and urban wastewater, contributing to metal pollution, were thoroughly assessed. The chapter also explored the superior mechanisms which control their behavior and bioavailability in aquatic environments, including the process of complexation with both the organic and inorganic ligands, redox reactions, and interactions with sediment particles. Additionally, the chapter investigated how environmental factors like pH, temperature, and hydrodynamic conditions alter the transport dynamics and transformation of metals in water bodies. Furthermore, the chapter addresses the role of particulate transport, colloidal transport, formation of metal-organic complexes, and dynamics of sedimentation and resuspension, besides bio-uptake and trophic transfer. This chapter integrates scientific data and case studies to provide comprehensive insights into heavy metal dynamics as well as their environmental consequences, highlighting critical areas for future research and policy development.