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Conowingo Dam Report Shows Time is Now for Collaboration, Innovation on Chesapeake Bay Cleanup

Scouring Nutrients and Sediment May Affect Implementation of Bay GoalsConowingo Dam

A newly finalized report on the Conowingo Dam underscores the urgency of finding innovative multi-state solutions to reduce the water pollution that threatens the Chesapeake Bay. The Lower Susquehanna River Watershed Assessment Study ─ conducted by the U.S. Army Corps of Engineers in coordination with the state of Maryland ─ confirms that the Conowingo Dam reservoir and two dam reservoirs further upstream have essentially reached their capacity and are no longer capable of trapping sediment and associated nutrients over the long term.

The assessment also found that the sediment and nutrients swept over the dams during large storm events are among the pollution sources that should be addressed to protect water quality and aquatic life in the Chesapeake Bay. Another major finding is that nutrients that enter the river upstream of the dams – from Pennsylvania and New York – and attach to sediment particles before flowing downstream into the bay have a larger impact on water quality than sediment itself.

“Maryland stands ready to work in collaboration with our upstream neighbors and federal partners to fix the shared sediments and associated nutrients problem,” Maryland Environment Secretary Ben Grumbles said. “We must all embrace innovative and cost-effective solutions to ensure the cleanup of the Chesapeake Bay and reduce the Conowingo’s impact on meeting our water quality standards in all bay segments.”

Modeling analysis shows that while sediments generally settle out of the water column within days or weeks, nutrients attached to the sediment can fuel algal growth and contribute to lower dissolved oxygen levels affecting water quality and underwater ecosystems. As a result, even with full implementation of Maryland’s federally-required bay cleanup plan, it will not be enough to achieve water quality standards in the three upper and mid-bay segments without strong actions from upstream states between 2017 and 2025.

The Environmental Protection Agency has established water pollution limits, the Chesapeake Bay Total Maximum Daily Load, which must be met by 2025 by Maryland and other bay watershed states. The EPA has said it would consider increasing its expectations for states’ progress in bay cleanup efforts if monitoring indicates that the Conowingo Dam’s capacity to trap sediment is reduced, as the newly finalized study shows. Maryland expects that the EPA will give new consideration to these findings since it was previously assumed that the Conowingo Dam would not lose its capacity for 15 to 30 years.

“We are grateful for the hard work and energy put into this report, but, action cannot end here,” Maryland Natural Resources Secretary Mark Belton said. “Maryland has worked hard to meet our Chesapeake Bay goals so it is critical that we acknowledge that the sediment and nutrients coming from these dams greatly impact our state’s waters. They may even prevent us from meeting our Chesapeake Bay goals. We are therefore committed to working hand in hand with our state and federal partners and Exelon to resolve this issue.”

The assessment also recommends that the state and partners carry out more Lower Susquehanna River monitoring and modeling to better measure medium to high flow event impacts on the bay. It also suggests that these results be used to inform the midpoint assessment. In an effort to be proactive, Maryland agencies, federal partners and Exelon heeded these suggestions from the early assessment and initiated a Lower Susquehanna River enhanced monitoring and modeling effort in 2015.

Maryland has been a leader in promoting viable management solutions like increased nutrient and sediment reduction practices, land conservation, dredging and beneficial reuse of dredged material, public-private partnerships, and market-based interstate water quality trading.


Environment:  Jay Apperson, 410-537-3003,

Natural Resources:  Karis King, 410-260-8001,




  • Meghan Graff Parker

    There is a train that idles for DAYS spewing air pollution with the possibility of a major environmental disaster in Port Deposit along the Susquehanna River. Residents have complained for years, yet nothing has been done. There was a near miss last fall, and the air alone is horrible when they are there. This is one place to start! Its unnecessary for them yo sit there AND to idle!

  • Phil Civitarese

    Conowingo dam
    huge environmental mistake
    the real solution is to take it out and get the natural flow going again.
    maybe then the shad and other fish might have a chance. In my 58 years of life I’ve seen our bay and tributaries poisoned by agricultural runoff from current farming techniques. The magic that was the Transquaking river, chicamicomico and may many others are near dead compared with the life they supported only 3 decades ago. Sad that new generations will not experience the magic of the yellow perch spawn, the shad runs and the incredible life that was once the chesapeake bay.
    Phil Civitarese

    • TrailsofBlood

      Pasture based agriculture replacing the current hog farming operations in Pennsylvania is the first step toward lowering the nutrient load. Increasing forest buffers and wild grass buffers around crop fields to soak up nutrients is next. However, nobody seems to have a good solution for the tons of silt backed up behind the dam.

  • Tom Zolper

    If you take time to read the actual report, or at least the Executive Summary, you will see that the authors say the most cost-effective way to deal with the problem is go upstream and prevent pollution entering the Susquehanna (farms, cities, etc.). This conclusion isn’t clear in the DNR communications about the issue.

  • richard fiedler

    what involvement does Pa. and NY have with controlling this problem. Seems to me that us Marylander’s are blamed for the bay’s pollution. would love to hear an answer

    • kking13

      Hi Richard,
      Thanks for your inquiry. Pennsylvania and New York are governed under the EPA Chesapeake Bay Total Maximum Daily Load (TMDL) requirements.

      All six Chesapeake Bay watershed states — MD, PA, NY, WV, VA, DE and the District of Columbia — are responsible for meeting nitrogen, phosphorus and sediment load reductions. Each jurisdiction’s mandated load reduction will ensure that the bay will meet its water quality standards by 2025 in support of adequate underwater grasses, fish, shellfish and other aquatic resources. Each Bay watershed state is tracked on progress towards meeting the nutrient and sediment load allocations by EPA.

      More information on the Bay TMDL and each states progress, including PA and NY can be found on the EPA Chesapeake Bay Program website at

  • jcwolf26

    I’m receiving a broken link when trying to access the Report. Has it been moved?