Allegheny River Lock and Dam No. 4
Why it's listed
Lock and Dam No. 4 sits on the Allegheny River in Natrona, Allegheny County, about 24.2 miles upstream from the river's mouth. The U.S. Army Corps of Engineers built it in 1920-1927 with its own hired labor after contract bids came in far above estimates. The facility created slackwater navigation for commercial barges and towboats along a stretch of roughly 72 miles of the river and gave steel mills at Natrona and a rail distribution center at Freeport water access. The lock measures 56 by 360 feet with a lift of 10.6 feet. Its two-story Moderne concrete operations building has a rounded upstream end. After the St. Patrick's Day flood of 1936 weakened the dam's south abutment, reconstruction in 1937-1938 added steel sheet piling and roughly 2.5 acres of derrick stone. The lock is regarded as a representative example of 1920s lock and dam construction.
Significance in brief: The nomination argues the lock and dam is significant under Criterion A as part of the Allegheny River slackwater navigation system, which allowed barge access and industrial growth along the lower river from Natrona to Freeport. It is also argued to be significant under Criterion C as a representative example of lock and dam construction of 1920-1927, retaining its original appearance and function with a high degree of integrity.
Machine-generated summary. This summary was generated by a language model from the official nomination document and has not been reviewed line by line by an editor. It may contain errors. Check the source document before relying on any detail. Source: nomination document (PDF) · National Archives catalog entry. NRHP reference 00000398, listed April 21, 2000. Summary generated October 2026 (model claude-haiku-5-5, prompt v1.1-2026-10-29, confidence high).
Key facts
| Address | 1 River Ave., Natrona |
|---|---|
| County | Allegheny County |
| Listed | April 21, 2000 |
| Reference number | 00000398 |
| Resource type | Structure |
| Period of significance | 1920-1927 |
| Architect / builder | U.S. Army Corps of Engineers (not contracted) |
| Architectural style | Moderne |
| Criteria |
|
| Areas of significance | Transportation, Maritime History, Economics, Engineering |
| Level of significance | State |
| Status (as stated in the nomination) | Operating lock; the locktender's house is presently vacant and the powerhouse has been altered, with gates and valves converted to electric operation in 1994-1995. |
| Acreage | 11.3 |
| Coordinates | 40.61334, -79.71602 (NPS GIS) |
What listing means for this property
For a publicly owned building or structure, listing mainly matters when federal funds, permits or licences are involved: projects then go through Section 106 review so effects on the property are considered. Listing also strengthens applications for preservation grants and, for leased income-producing uses, can enable the federal rehabilitation tax credit.
General information, not legal or tax advice. Rules change; confirm with your State Historic Preservation Office or a qualified adviser.
Sources and further reading
- National Park Service, National Register of Historic Places database (snapshot May 2026), reference 00000398.
- Nomination form (PDF, National Archives) — catalog entry
- Wikipedia article (used for cross-checking only; text not reproduced here)
- Wikidata Q4731336
- This listing as JSON
Last updated October 2026. Found an error? See the editorial policy for how to report it.