Sediments are widely recognized as one of the most valuable natural archives for reconstructing environmental change and assessing pollution in aquatic ecosystems. Acting both as sinks and secondary sources of contaminants, sediments accumulate pollutants over time, preserving a historical record of natural processes and anthropogenic activities. This unique characteristic makes sediments powerful geomarkers for evaluating the spatial and temporal distribution of environmental contaminants in marine, estuarine, riverine, and lacustrine environments. This presentation explores the concept of sediment as a geomarker and highlights its significance in modern pollution studies. Particular emphasis will be placed on the role of sediment in recording contamination from potentially toxic elements (PTEs), including mercury, cadmium, lead, arsenic, chromium, copper, zinc, and nickel, as well as emerging pollutants such as pharmaceuticals, microplastics, and persistent organic contaminants. Through physical, chemical, and geochemical characterization, sediment provides critical information on pollutant sources, transport pathways, accumulation patterns, and long-term environmental trends. This study will discuss key approaches used in sediment-based pollution assessment, including sediment core analysis, geochemical normalization, enrichment factor determination, contamination indices, isotopic fingerprinting, and multivariate statistical techniques. These tools enable researchers to distinguish natural geological inputs from human-induced contamination and to reconstruct pollution histories spanning decades to centuries. Furthermore, advances in environmental geochemistry and geospatial technologies have enhanced the reliability of sediment for environmental monitoring and management. Beyond contamination assessment, sediment offer valuable insights into ecological and human health risks by identifying pollutant hotspots, evaluating bioavailability, and predicting potential remobilization of contaminants under changing environmental conditions. As coastal development, industrialization, urbanization, and climate-related disturbances continue to intensify worldwide, the need for robust and cost-effective monitoring tools becomes increasingly important. By viewing sediments as environmental archives rather than merely depositional materials, this presentation demonstrates how sediment can serve as indispensable tools for pollution surveillance, environmental forensics, ecosystem protection, and evidence-based policy development. Ultimately, understanding the stories preserved within sediment layers allows us to better reconstruct the past, assess the present, and safeguard the future of aquatic environments.