Flood water: Toxins from the riverbed

A long-term hazard from flood water is often underestimated: The raging rivers swirl up pollutants out of their sediments that stem from environmental pollution decades or centuries ago. Such harmful substances can not only cause ecological damage in the river. They can also deposit themselves on flooded areas and affect crops, grazing livestock and humans.

source https://www.sciencedaily.com/releases/2021/08/210802140140.htm