{"nrhp_refnum":"84003774","name":"Lake Hamilton Dam","other_names":["Hamilton Lake Dam"],"category":"structure","location":{"address":"1.5 miles NE of Poland off SR 616","address_restricted":false,"city":"Struthers","county":"Mahoning County","state":"OH","lat":41.03694465800004,"lon":-80.59161918099994,"geom_source":"nps_gis"},"listed_date":"1984-05-07","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Industry","Engineering"],"significance_levels":["local"],"summary":{"what_it_is":"A masonry gravity dam, with its spillways, gatehouse and aqueduct, on Yellow Creek about 1.5 miles northeast of Poland, in Struthers, Mahoning County, Ohio. Construction ran from June 1906 to 1907 for the Mahoning Valley Water Co.","why_significant":"The nomination argues the dam is among the finest examples of massive Ashlar sandstone masonry dam construction in Ohio and the United States. It is also one of the earliest dams to use cyclopean concrete backing. Locally, it supplied water for iron and steel production, notably for Youngstown Sheet and Tube Co., in the Mahoning Valley.","narrative":"Lake Hamilton Dam is a 70-foot-high gravity dam on Yellow Creek in Struthers, Ohio, built between 1906 and 1907 to a design by civil engineer David M. Wise. Its core is cyclopean concrete, faced with precisely cut Ashlar sandstone quarried near New Castle, Pennsylvania. The dam is 262 feet long and holds back a 136-acre lake. Related features include two spillways, a sandstone gatehouse, a tunnel and a sandstone aqueduct. The nomination describes it as the tallest and largest masonry dam in Ohio and an outstanding example of stonework, with no alterations to the dam itself. It was among the earliest masonry dams to use cyclopean concrete fill. The dam also mattered to industry: it supplied water to the iron and steel mills of Youngstown and the Mahoning Valley, including Youngstown Sheet and Tube Co. Since 1922 the grounds have also served recreational uses.","period_of_significance":"1900-","architect_builder":"David M. Wise (civil engineer, designed 1904); Mahoning Valley Water Co.; William McIntyre Sons & Co., contractors","architectural_style":null,"criteria":["A","C"],"status_note":"Condition listed as excellent and unaltered; the surrounding area opened to the public in 1922 for fishing, hiking and picnicking, and the dam is used for water supply.","vacant_flag":false,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:53:14.812873-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/lz/electronic-records/rg-079/NPS_OH/84003774.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/84003774/8e7e5a89f0-800.webp","url_1600":"https://nationalhistoricalregister.com/media/84003774/8e7e5a89f0-1600.webp","licence":"Public domain","author":"Nyttend","credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:Lake_Hamilton_Dam.jpg\" rel=\"noopener\">Nyttend</a>, Public domain, via Wikimedia Commons","source_page":"https://commons.wikimedia.org/wiki/File:Lake_Hamilton_Dam.jpg"},"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/71990144","wikipedia":null,"wikidata":"https://www.wikidata.org/wiki/Q35707016"},"indexable":true,"url":"https://nationalhistoricalregister.com/ohio/mahoning-county/lake-hamilton-dam-84003774/"}