{"nrhp_refnum":"73001289","name":"Old Croton Dam, Site of","other_names":["New Croton Dam","See Also:Downtown Ossining Historic District"],"category":"site","location":{"address":"N of Ossining on NY 129","address_restricted":false,"city":"Ossining","county":"Westchester County","state":"NY","lat":41.22623400700007,"lon":-73.85541349099998,"geom_source":"nps_gis"},"listed_date":"1973-06-19","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Engineering","Architecture"],"significance_levels":["national"],"summary":{"what_it_is":"The submerged site of the Old Croton Dam, a masonry gravity dam built 1837-42 in the Yorktown/Ossining area of Westchester County, New York, nominated together with the nearby New Croton Dam built 1893-1906.","why_significant":"The Old Croton Dam was the first large masonry dam in the United States and a model for municipal water supply dams in the eastern states. It was the key link to the Old Croton Aqueduct and is notable as an intact underwater archeological site. The New Croton Dam is cited as a major engineering work of notable design and as the largest pure masonry dam.","narrative":"Beneath the waters of the New Croton Reservoir in Westchester County lies the Old Croton Dam, built between 1837 and 1842 under engineer John Bloomfield Jervis. A gravity dam of rubble core with granite ashlar facing, it ran 670 feet long and 57 feet high, backing the Croton River up about five miles to form a reservoir of roughly 400 acres. It fed the Old Croton Aqueduct, which brought water to New York City. Described as the first large masonry dam in the United States, it served as a model for later municipal water supply dams in the east. When the New Croton Dam was completed in 1906, the older structure was submerged, though it remains intact and was briefly exposed in 1956. The nomination also covers the New Croton Dam, a 1,168-foot masonry structure with buttresses, arches, a curved spillway and a steel arch bridge, praised for combining engineering with architectural design beside Croton Gorge park.","period_of_significance":"1837-42 (Old); 1893-1901-06 (New)","architect_builder":"John Bloomfield Jervis (Old Dam engineer in charge); New Dam engineers Alphonse Fteley, William R. Hill, J. Waldo Smith and Walter H. Sears","architectural_style":null,"criteria":[],"status_note":"Old dam is submerged in the New Croton Reservoir and still intact; it was exposed briefly when the reservoir was lowered in 1956. New Croton Dam remains part of the New York City water supply, rated excellent condition.","vacant_flag":null,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:50:38.922706-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/lz/electronic-records/rg-079/NPS_NY/73001289.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/73001289/79a33b698b-800.webp","url_1600":"https://nationalhistoricalregister.com/media/73001289/79a33b698b-1600.webp","licence":"CC BY-SA 2.0","author":"Patrick Stahl","credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:Croton_Reservoir.jpg\" rel=\"noopener\">Patrick Stahl</a>, <a href=\"https://creativecommons.org/licenses/by-sa/2.0\" rel=\"license noopener\">CC BY-SA 2.0</a>, via Wikimedia Commons","source_page":"https://commons.wikimedia.org/wiki/File:Croton_Reservoir.jpg"},"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/75323145","wikipedia":"https://en.wikipedia.org/wiki/Old_Croton_Dam","wikidata":"https://www.wikidata.org/wiki/Q7531782"},"indexable":true,"url":"https://nationalhistoricalregister.com/new-york/westchester-county/old-croton-dam-site-of-73001289/"}