ince its construction as a hydroelectric plant in 1928, the Conowingo
Dam on the Susquehanna River in Maryland has been trapping pollution flowing down the Susquehanna River from New York and Pennsylvania
in the reservoir behind the structure. In the mid-1990s, researchers estimated that the Conowingo Dam and two upstream dams were trapping about 40 percent of the phosphorus and 70 percent of the suspended sediment that would have otherwise entered the Bay.
Today, researchers estimate the Conowingo Dam reservoir is almost
completely filled. As a result, the dam has lost much of its capacity
to trap. During big storms when the flow through the dam is high,
trapped pollution, including phosphorus-laden sediment, is washed
from the reservoir into the river below, contributing additional pollution downstream and into the Chesapeake Bay.
As the regional watchdog for the Chesapeake Bay, CBF is seeking a
comprehensive solution to this problem, one that addresses the pollution build-up at the dam, the pollution entering the Susquehanna
upstream, and the need to enhance fish passage for migrating species.
CBF filed to intervene in the relicensing of the dam, owned by
Exelon Corporation, whose current license expires on September 1,
2014. This intervention will ensure CBF continues to be involved
when the Federal Regulatory Energy Commission negotiates and
sets the conditions for Exelon’s new license. We will be positioned
for a legal challenge, if necessary.
“The public can rest assured many eyes will continue to scrutinize
this process. The Susquehanna is getting cleaner, and we will insist
the trend continue, just as we are pushing for cleaner creeks and
rivers throughout the Chesapeake Bay area,” said Kim Coble, CBF
Vice President for Environmental Protection and Restoration.
The management of the sediment in the Conowingo reservoir is an
important part of future strategies for reducing pollution. A comprehensive solution must include a significant role for Exelon, as
well as continued reduction of pollution from New York,
Pennsylvania, and Maryland to the Susquehanna River and to the
The Conowingo Dam and the Chesapeake Bay
S The Dam Facts
1. The dam is not the largest source of pollution to
the Bay, the Susquehanna River is. The Susquehanna
contributes roughly 33% of the sediment, 25% of the
phosphorus, and 46% of the nitrogen flowing into
2. The dam has little impact on nitrogen pollution
loads, which are showing a downward trend on the
Susquehanna. Nitrogen is water soluble so little is
trapped behind the dam, unlike sediment and phosphorus (which is often attached to sediment). Therefore,
even if the reservoir completely filled, the amount of
nitrogen reaching the Bay would continue to decrease
due to implementation of upstream pollution-reduction
3. The Susquehanna mostly affects the central stem of
the Bay. Many of Maryland's local creeks and rivers
are on the EPA’s “impaired waters list” and are polluted
almost entirely by local sources—farms, sewage plants,
septic systems, urban and suburban runoff, and other
sources, which must be addressed locally.