The Conejohela Flats are a group of islands in the flooded Conejohela Valley, a large floodplain along the southernmost 30 miles (50 km) of the

Susquehanna River The Susquehanna River ( ; Unami language, Lenape: ) is a major river located in the Mid-Atlantic (United States), Mid-Atlantic region of the United States, crossing three lower Northeastern United States, Northeast states (New York, Pennsylvani ...

Pennsylvania Pennsylvania, officially the Commonwealth of Pennsylvania, is a U.S. state, state spanning the Mid-Atlantic (United States), Mid-Atlantic, Northeastern United States, Northeastern, Appalachian, and Great Lakes region, Great Lakes regions o ...

and

Maryland Maryland ( ) is a U.S. state, state in the Mid-Atlantic (United States), Mid-Atlantic region of the United States. It borders the states of Virginia to its south, West Virginia to its west, Pennsylvania to its north, and Delaware to its east ...

in the United States. The valley was flooded primarily during the early 1900s by the construction of the Holtwood, Conowingo, and Safe Harbor dams from 1910 to 1931.

Geography and history

Before the twentieth century, the Conejohela Valley was a marshy floodplain, with extensive wetlands. The Susquehanna River flooded annually in the spring, and there were more damaging floods approximately once per decade. Thick forests surrounded a mixture of small waterfalls, rapids, and marshes. A wide, flat valley formed; the frequently wide river was a substantial barrier to crossing, both for Native Americans and for colonists. The varied terrain created many nurturing biological habitats, but human passage across the valley and river was extremely difficult. The Susquehanna is very wide in this area, as it nears its mouth on the

Chesapeake Bay The Chesapeake Bay ( ) is the largest estuary in the United States. The bay is located in the Mid-Atlantic (United States), Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula, including parts of the Ea ...

. This stifled trade across the lower Susquehanna in colonial

and

. In 1730, the

Wright's Ferry Wright's Ferry was a Pennsylvania Colony settlement established by John Wright in 1726, that grew up around the site of an important Inn and Pub anchoring the eastern end of a popular animal powered ferry (1730–1901) and now a historic part ...

was established to cross the river. Later the first Columbia-Wrightsville Bridge was built, once believed to be the longest covered bridges in the world. It was replaced by bridges built of structural steel, large enough to carry a range of vehicles. The modern bridge opened in 1930; it was dedicated in 1980 as the Veterans Memorial Bridge.

Flooding

Three dams were built across the Conejohela Valley during the first four decades of the 20th century to provide hydroelectric power for southern Pennsylvania (including electrical power for Amtrak and SEPTA Regional Rail) and to control the annual flooding. It also had the unintended consequence of preventing sediment from the Flats and points upstream from reaching the

. The first dam across the lower Susquehanna, the

Holtwood Dam Holtwood Dam (also Holtwood Hydroelectric Dam, Holtwood Hydroelectric Plant, McCalls Ferry Dam) is the oldest of three major dams built across the lower Susquehanna River, and the middle location of the three. It was constructed as the McCalls Fer ...

, was completed in 1910 as McCalls Ferry Dam. The

Conowingo Dam The Conowingo Dam (also Conowingo Hydroelectric Plant, Conowingo Hydroelectric Station) is a large hydroelectric dam in the lower Susquehanna River near the town of Conowingo, Maryland, Conowingo, Maryland. The medium-height, masonry gravity dam ...

followed in 1928. The Safe Harbor Dam had the largest effect on the river ecosystem. When it first closed its gates on September 29, 1931, it flooded more than 10 miles of the upper Conejohela Flats, creating the artificial Lake Clarke. Most of the valley was flooded. The few islands that remain in Lake Clarke are a gathering of low, marshy flats about five miles north of Safe Harbor Dam.

Habitat

The remaining Conejohela Flats provide habitats for a number of species. The varying depths of inundated islands on the bottom of Lake Clarke support numerous fresh water feeder fish, pan fish, and large predatory

game fish Game fish, sport fish or quarry refer to popular fish species pursued by recreational fishing, recreational fishers (typically angling, anglers), and can be freshwater fish, freshwater or saltwater fish. Game fish can be fish as food, eaten aft ...

species. The Safe Harbor Dam has become a popular area for local fishing. The low-lying islands and

riparian A riparian zone or riparian area is the interface between land and a river or stream. In some regions, the terms riparian woodland, riparian forest, riparian buffer zone, riparian corridor, and riparian strip are used to characterize a ripar ...

ecosystem also support dozens of species of birds; the flats are popular among birders.

References

External links

Safe Harbor Water Power Company
{{authority control Susquehanna River Crossings of the Susquehanna River Landforms of Lancaster County, Pennsylvania Landforms of York County, Pennsylvania Islands of Pennsylvania

Geography and history

Flooding

Habitat

See also

References

External links