Humans have affected lakes and rivers in Canada through numerous activities, including large-scale disturbances such as clearing forests, building cities, and discharging pollution into water bodies. For most lakes, we have a difficult time figuring out what environmental impact these activities have had, as large-scale European immigration into Canada started in the 19th century, yet it is only the last few decades that we have been measuring environmental conditions in lakes. The examination of fossil remains preserved in lake mud provides important clues in determining how we have affected our freshwater ecosystems.