This lecture explores how sediments in lakes act as a historical record of water quality, reflecting regional and point source pollutions, industrial activities, and paleo pH and temperature. It discusses the accumulation of pollutants like Zn, DDT, and PCBs in lake sediments, providing insights into past industrial, mining, and urban pollution. The lecture also covers the use of sediments to study prehistorical mining activities, Inca mining culture, and surface water paleo temperature and pH values.