When the Conowingo Dam opened to fanfare nearly a century ago, the massive wall of concrete and steel began its job of harnessing water power in northern Maryland. It also quietly provided a side benefit: trapping sediment and silt before it could flow miles downstream and pollute the Chesapeake Bay, the nation's largest estuary. The old hydroelectric dam spanning the lower Susquehanna River is still producing power, but its days of effectively trapping sediment in a 14-mile long reservoir behind its walls are over. Behind the 94-foot-high barrier lies a massive inventory of coal-black muck—some 200 million tons of pollutants picked up over decades from farmlands, industrial zones, and towns, the AP reports.
How big a threat this sediment stockpile poses to the Chesapeake Bay or whether anything can even be done depends on who one talks to, but intense cycles of downpours are washing pollutants into the Chesapeake from municipal sewer overflows, subdivisions, and farms where manure often isn't effectively handled and nitrogen and phosphorous-rich fertilizers are used. Experts say climate change is accelerating the environmental decline, potentially leading to more damaging algae blooms and dead zones in the Chesapeake and coastal waters. With Maryland pushing to curb pollution in dam discharges, the issue has become a political football as Conowingo's operator seeks to renew its federal license to operate the dam for 46 more years after its old license expired.
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