By Alex DeMetrick

DARLINGTON, Md. (WJZ) — Recent signs the Chesapeake Bay is getting healthier also comes with signs a major threat of pollution sits right behind the Conowingo Dam.

Alex DeMetrick reports, the decades-old dam turns water into electricity, but that benefit also comes with a risk.

More than water is now spilling over the lip of the dam. Behind it, decades of sediment has been piling up.

Soil washed off land in New York and Pennsylvania once blocked, is now able to spill over.

“Conowingo Dam reservoir has reached capacity and is no longer able to trap sediment,” says Governor Larry Hogan.

Hogan recently took his own aerial tour of the dam, which sits in the lower Susquehanna River, which feeds into the top of the bay.

Recent gains in water quality have reduced massive algae blooms and dead zones, and brought underwater grasses back. Those gains, “could be wiped out with the effects of one bad storm,” Hogan says.

As it did in 2011, when Tropical Storm Lee swamped the bay with sediment from the Susquehanna. The sediment plume stretched south to the Potomac River.

“There was major sedimentation,” says Rob Newberry, of the Delmarva Fisheries Association. “Destroyed vast areas of oyster bottom and stuff like that. And it’s something that has to be addressed.”

But even during Lee, the dam was still blocking some sediment. But now now, with 25 million cubic yards behind the dam, which could cost $3 billion to dredge.

Meanwhile, 3 million cubic yards per year is still coming downstream.

So Maryland is looking for bidders to take on an experiment to remove sediment at less cost.

“A project of 25,000 cubic yards of dredging behind Conowingo Dam,” says Roy McGrath, Director of Maryland Environmental Service. “Something like this has never been done before.”

If the dredging experiment works, the results should be known by next March.

The state will pay for the demonstration project, but will be looking to Exelon, which owns the dam, and the federal government, to join in funding a full scale project.

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