Seneca Aqueduct

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Seneca Aqueduct
The Seneca Aqueduct in 1936, before collapse
Seneca Aqueduct today
The Seneca Aqueduct today

Seneca Aqueduct — or Aqueduct No. 1 — carries the Chesapeake and Ohio Canal over Seneca Creek (Potomac River) in Montgomery County, Maryland. The C&O built eleven aqueducts along its 184.5 miles. Seneca Aqueduct is a unique structure, not only being the first built, but also the only red sandstone aqueduct on the C&O - and the only aqueduct that is also a lock (Lock 24, or Riley's Lock). It is located at the end of Riley's Lock Road in Seneca, Maryland.


Seneca Aqueduct was built from 1828-1833 with three red sandstone arches quarried in the nearby Seneca Quarry, just a few hundred feet to the west. The initial stretch of the C&O Canal opened in 1830 up to Seneca Creek; the next segment opened from Seneca to Harpers Ferry in 1833. This included a sizable turning basin, just west of the aqueduct, where canal boats could anchor or turn around. Next to the aqueduct and lock is the lock keeper's house, also made from Seneca red sandstone. Because of the canal, the nearby quarry operations, and additional mills on Seneca Creek, the town of Seneca was an active working class community.

In 1897, the steam packet boat Anna Wilson leaving the aqueduct, collided with a freight boat loaded with watermelons, and sank. There were no injuries to the passengers. Local residents had "a ball" fishing out the watermelons floating in the basin.[1]

The canal closed in 1924 after ninety-six years in operation.

A major flood in September 1971 took out the westernmost of the three arches. The National Park Service has since shored up the aqueduct with steel beams.[2]

After a 1971 flood destroyed part of the Seneca Aqueduct, steel beams were added to shore up the structure.

Seneca Aqueduct is part of the C&O Canal National Historic Park and is administered by the National Park Service. The aqueduct is included in the Seneca Historic District in Montgomery County, Maryland.

Boat entering Riley's Lock (Seneca Aqueduct)


  1. ^ Hahn, Thomas Towpath guide to the Chesapeake & Ohio Canal; Georgetown Tidelock to Cumberland American Canal and Transportation Center, 1993. ISBN 9780933788664, p. 67
  2. ^ Peck, Garrett (2012). The Potomac River: A History and Guide. Charleston, SC: The History Press. pp. 62–63. ISBN 978-1609496005. 

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Coordinates: 39°4′7.45″N 77°20′28.22″W / 39.0687361°N 77.3411722°W / 39.0687361; -77.3411722