In the Susquehanna River, there is much polluted sediment build up compiled and slowly seeping into the Chesapeake Bay. However, large portions of the sediment are still compacted at three hydroelectric dams along the river in Pennsylvania and Maryland: Safe Harbor Dam, Holtwood Dam and Conowingo Dam. At these dams, much of the collected mud holds many pollutants, such as heavy metals, fertilizers, coal dusts, and waste. Most dangerous to the river and bay habitats, Phosphorous is also found trapped in the sediment behind these dams. In 1972, Tropical Storm Agnes released thousands of tons of this sediment into the bay ecosystem. There is much concern that another storm could let loose some or all of the remaining thousands of tons of this polluted mud.