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Experts Warn of 'Dead Zone' in Chesapeake Bay


Officials once counted on Conowingo Dam to block large amounts of sediment in the Susquehanna from reaching Chesapeake Bay, the nation's largest estuary, but the reservoir behind the dam has filled with sediment far sooner than expected. (AP Photo/Steve Ruark)
Experts Warn of 'Dead Zone' in Chesapeake Bay
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The Chesapeake Bay is the largest estuary in the United States.

To nature lovers, the bay is a national treasure. Its waters are perhaps best known for blue crabs and oysters.

For many years, the Chesapeake Bay area benefited from the Conowingo Dam on the Susquehanna River. When the dam opened nearly 100 years ago, it began controlling the power of water to create electricity for northern Maryland. It also trapped sediments before they reached the bay’s waters.

While the old dam is still making electricity, it no longer helps the Chesapeake. It cannot. Behind its heavy walls lie 181 million metric tons of black muck – pollutants it has collected since the day the dam opened.

Now some people fear that the black muck may be a threat to the bay. Recent heavy rains have shown that muck runoff can move along the sides of the dam and pollute the water. The lack of agreement on the best way to stop the muck from polluting the Chesapeake, shows how fragile the area really is.

In 1983, the U.S. government launched a clean-up program that ended years of uncontrolled pollution. The cleanup has been considered a great success, with blue crabs and oyster populations expanding.

But experts say heavy rainfall is causing runoff pollutants from all over the area to reach the bay. They say this could lead to large dead zones in the waterway.

Operators of the Conowingo Dam want to extend its operating permit and keep the dam working for another 46 years. Many Maryland environmentalists say the black muck behind the dam is just one example of severe threats to the Bay. If a major storm enabled the black muck to flow freely into the bay, it would destroy the water’s ecosystem.

“The situation behind the dam is a…time bomb,” said Genevieve Croker. She is with the Clean Chesapeake Coalition, a group fighting to keep the bay clean.

Water flows through Conowingo Dam, a hydroelectric dam spanning the lower Susquehanna River near Conowingo, Md., on Thursday, May 16, 2019. (AP Photo/Steve Ruark)
Water flows through Conowingo Dam, a hydroelectric dam spanning the lower Susquehanna River near Conowingo, Md., on Thursday, May 16, 2019. (AP Photo/Steve Ruark)

Qian Zhang is a research scientist at the University of Maryland Center for Environmental Science. He agrees that the runoff is a problem, but says the muck is not the greatest threat to the bay.

Nutrient pollution, the chemical runoff from farms, is a much bigger worry, he believes. Most of the nutrient pollution comes from farms in the state of Pennsylvania, just north of Maryland. It flows down the Susquehanna River to the bay.

William Ball is a scientist with the Chesapeake Research Consortium. He said the best way to stop pollutants from entering the bay is to “better manage upstream sources.”

Deborah Klenotic is a spokeswoman for Pennsylvania’s Department of Environmental Protection. She says her state is working hard to meet its target for pollution reduction. The efforts, she said, “have never been stronger.”

But this work may not be enough. Scientists are warning that there will be a 3 kilometer area of no oxygen in the Chesapeake Bay this year. That would make it one of the largest ‘dead zones’ in nearly 20 years.

I’m Susan Shand

The Associated Press reported this story. Susan Shand adapted the report for VOA Learning English. George Grow was the editor.

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Words in This Story

estuary – n. an area where a river flows into the sea

benefit – v. a good or helpful result or effect

sediment – n. material (such as stones and sand) that is carried into water by water,

muck – n. wet dirt or mud

fragile – adj. easily broken or damaged

zone – n. an area that is different from other areas in a particular way

ecosystem – n. everything that exists in a particular environment

manage – v. to have control of something

source – n. the beginning of a stream or river of water

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