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Located in York County, PA, the Lake Williams Dam has supplied water to its surrounding communities for over 113 years. Constructed, owned, and operated by The York Water Company, the dam forms a 220-acre lake within William H. Kain County Park. Despite the dam’s structural soundness, the requirement to safely pass a Probable Maximum Flood of over 107,000 cubic feet per second – an exponential increase to its originally-designed capacity – prompted a rehabilitation that commenced in 2022 and was substantially completed by the end of 2023. To meet an expedited schedule for planning, design, permitting, and construction, York Water, Gannett Fleming, and the contractor worked together to reimagine a dam that would meet modern design, safety, and performance standards. The resulting rehabilitation consisted of a new roller-compacted concrete labyrinth spillway and embankment overtopping protection, a new intake tower and low-level outlet works, a stream crossing downstream of the dam, and several environmental enhancements that will ensure the dam’s ability to provide essential water services for another century, while also increasing the storage of Lake Williams by raising the normal pool reservoir elevation by one foot. This presentation will discuss the history of the dam, rehabilitation objectives, design considerations, construction challenges and solutions, and lessons learned.