House rock overlook

House Rock on the Susquehanna River in Martic Township.

The Susquehanna River has been named the third most-endangered river in the United States in an annual list by the environmental group American Rivers.

The group selected the Susquehanna primarily because of what it called the detrimental effects from the Conowingo Dam, just below the Lancaster County line in Harford County, Maryland.

“The Conowingo Dam alters river flow, blocks fish and impacts water quality, harming the Susquehanna and the Chesapeake Bay downstream,” the group said.

The group also cited the well-documented concern that the dam is now no longer trapping sediment containing nitrogen and other pollutants.

Since its construction in 1928, the dam has trapped pollutants coming downstream in sediment running off farm fields and other sources. But in recent years, scientists have warned that the capacity for trapping sediment is essentially exhausted.

Now, during floods, strong river currents scour sediment from the reservoir and flush them and their buried pollutants downriver and into the Chesapeake Bay.

No solution to the problem has been agreed on. The cost of fixing it would be high and just who should be responsible for doing the work continues to be debated.

“There is no doubt that the Susquehanna River is an endangered river,” said Kim Coble, vice president of the Chesapeake Bay Foundation, a private conservation group.

“It is the largest source of fresh water to the bay, as well as the largest source of nitrogen pollution. This pollution feeds the algal blooms and dead zones that hurt aquatic life. The Chesapeake Clean Water Blueprint requires all sources to reduce pollution, including Exelon.”

Exelon is the owner of the Conowingo Dam. The utility is currently working with various agencies in Maryland, Pennsylvania and the federal government for a new 46-year license.

American Rivers also said the Susquehanna is endangered by a bill in Congress that would take away Maryland’s authority to hold dam operators accountable for pollution and impacts to wildlife.

American Rivers said the bill, which has already passed the U.S. House of Representatives, “would not only exempt Exelon from meeting water quality standards, it would also transfer the responsibility for addressing the dam’s impacts to the bay’s municipalities, farmers and citizens.”

The bill is opposed by Maryland Gov. Larry Hogan, both state senators and seven of its eight U.S. representatives.

“The state is committed to addressing the potential environmental damage caused by the Conowingo Dam reaching capacity, and is partnering with the federal government and Exelon to address fish passage and water quality concerns as part of the relicensing process,” said Mark Belton, secretary of the Maryland Department of Natural Resources.