Conowingo Dam

Go to

Conowingo Dam, May 2019. Photo credit: John Pavoncello

The Conowingo Dam is owned and operated by Constellation (formerly Exelon Generation Company, LLC) and its federal license expired in 2014. Constellation sought a new 50-year license from the Federal Energy Regulatory Commission (FERC). Under Section 401 of the Clean Water Act, the State of Maryland had to issue a Water Quality Certification, certifying that the project will meet state water quality standards before FERC can grant a new license.

Waterkeepers Chesapeake has been working with Lower Susquehanna Riverkeeper and Earthjustice since 2014 to hold Exelon accountable for its fair share of the dam cleanup.

“This is our only opportunity in the next 50 years to get meaningful pollution reductions at Conowingo Dam – we have to hold Exelon accountable for its fair share of the cleanup,” — Betsy Nicholas, Former Executive Director, Waterkeepers Chesapeake.

Historic Win

In June 2021, Waterkeepers Chesapeake, Lower Susquehanna Riverkeeper and Sassafras Riverkeeper, represented by Earthjustice, and joined by Chesapeake Bay Foundation, challenged FERC’s 50-year dam license. On December 20, 2022, the U.S. Court of Appeals for the District of Columbia Circuit issued an opinion vacating the Federal Energy Regulatory Commission’s (FERC) licensing of the Conowingo Dam and remanded it back to FERC. In its decision, the court agreed with Waterkeepers Chesapeake, Lower Susquehanna Riverkeeper, ShoreRivers, and Chesapeake Bay Foundation’s argument that FERC exceeded its authority when it approved a 50-year license without including the Water Quality Certification that Maryland issued in 2018.


The State of Maryland issued its Water Quality Certification on April 27, 2018, and Exelon sued the State on May 25 in federal district court, challenging the state’s authority to require any pollution reduction from upstream sources. On July 20, 2018, Waterkeepers Chesapeake and Lower Susquehanna Riverkeeper, represented by Earthjustice, filed a motion to intervene in a federal court action regarding the relicensing of the Conowingo Dam, supporting the State’s authority under the Clean Water Act. This motion to intervene was denied.

In addition, Waterkeepers Chesapeake and the Lower Susquehanna Riverkeeper Association filed an administrative appeal on June 8, 2018, urging the Maryland Department of the Environment to reconsider its water quality certification for the Conowingo Dam arguing that it was missing several key elements. The appeal included a review of flawed conclusions in the Lower Susquehanna River Watershed Assessment (see FlowWest LSRWA Review, Aug 25, 2017). On October 29, 2019, MDE and Exelon announced a settlement agreement made behind closed doors that fell far short of protecting Maryland’s waterways and required the state to waive the Water Quality Certification it issued in 2018 that would have protected local water quality from impacts of dams, without any details on how the agreement will protect water quality. In addition, it provided grossly insufficient funds to deal with the risks that Conowingo operations pose to the Susquehanna River and Chesapeake Bay, and lacked concrete assurances that the actions under the agreement will actually be fulfilled by Exelon.

FERC Permit Challenge

In March 2021, FERC approved Exelon’s Conowingo relicensing for the next 50 years. This license includes the extremely flawed 2019 settlement agreement between the Maryland Department of the Environment (MDE) and Exelon. The timing of the relicensing decision derailed our efforts to pass bi-partisan emergency legislation that would have stopped the settlement agreement. In May 2021, the EPA’s evaluation of the Conowingo Watershed Implementation Plan (CWIP) noted that even though the financing plan is still in development, there’s a lack of confidence that this plan can be carried out without clear public funding sources identified. The earliest CWIP framework documents included Exelon as the likely source for funding the plan.

Conowingo Dam: Last Chance for a Fair Deal

Bay state taxpayers are now left with the responsibility of paying for the dam cleanup instead of requiring Exelon to pay its fair share. The Water Quality Certification that MDE issued in 2018 required $172 million per year just to reduce nitrogen and phosphorus pollution. The actual cost of meaningfully reducing the 200 million tons of nutrients and sediment behind the dam was estimated to be between $53 – $300 million per year in the CWIP. Read more in our CWIP Comments.

About the Conowingo Dam

The Conowingo Dam is located on the Lower Susquehanna River about 10 miles upstream from where it flows into the Chesapeake Bay at Havre De Grace, Maryland. As a hydropower dam, Conowingo has replaced a free-flowing section of the Susquehanna River with a 14-mile-long, 9,000-acre reservoir. This fundamentally alters the river’s ecology.

Ever since the dam was built in 1928, it has changed seasonal river flow; blocked the migration of shad, herring, eel and other fish; destroyed fragile aquatic habitat; devastated the shellfish communities that naturally filtered the Susquehanna’s water; killed millions of fish caught in hydroelectric turbines; and altered the river’s natural ability to transport nutrients and sediment. Because Constellation (formerly Exelon) did not maintain the dam’s reservoir, nearly 200 million tons of sediment pollution accumulated behind the dam. During major floods caused by large storms, powerful floodwaters can scoop out or “scour” the stored nutrient-laden sediment behind the dam and send that downstream to the Lower Susquehanna and the Chesapeake Bay.

The dam supplies power for the Muddy Run pump and storage facility, and provides cooling water to the Peach Bottom Nuclear Facility, all operated for a profit by Constellation (formerly Exelon). During peak power usage periods, the dam can provide power to homes and other buildings.

Waterkeepers Chesapeake Urges EPA to Fully Restore State, Tribal, and Community Rights Under the Clean Water Act’s Section 401

Waterkeepers Chesapeake Urges EPA to Fully Restore State, Tribal, and Community Rights Under the Clean Water Act’s Section 401

On August 8, 2022, Waterkeepers Chesapeake submitted comments to the U.S. Environmental Protection Agency (EPA) urging removal and replacement of regulations of ...
Waterkeepers Chesapeake logo

Md. Inaction Can’t Spur Dam Relicensing, DC Circ. Told –

Md. Inaction Can’t Spur Dam Relicensing, DC Circ. Told,, May 26, 2022, by Keith Goldberg The Federal Energy Regulatory ...
Support Grows for Lawsuit Over Conowingo Dam Pollution

Support Grows for Lawsuit Over Conowingo Dam Pollution

Several groups, legislators, and businesses support lawsuit challenging relicensing  (Takoma Park, MD) – Last Friday, three amicus briefs were filed ...
Forum: Conowingo Dam Cleanup: Why are you paying and Exelon isn't?

Forum: Conowingo Dam Cleanup: Why are you paying and Exelon isn’t?

Join the discussion on how we can still get a fair deal for the next 50 years. In March 2021, ...

Please consider a donation to support our work to get a fair deal on the Conowingo Dam cleanup!