Lake Williams, located in York Township, Pennsylvania, is a private water supply reservoir built in 1912 with a primary purpose of water supply. The dam, standing at 58 feet in height and 700 feet in length, holds a maximum storage capacity of 5,800 acre-feet and a normal storage capacity of 3,370 acre-feet. The reservoir covers a surface area of 165 acres and drains an area of 45 square miles, with the East Branch of Codorus Creek serving as the primary water source.

Despite its important role in providing water to the region, Lake Williams faces significant challenges as indicated by its high hazard potential and poor condition assessment. In 2010, structural modifications were made to address safety concerns. The dam is regulated by the Pennsylvania Department of Environmental Protection, with state permitting, inspection, and enforcement in place to ensure compliance with safety standards. The reservoir also offers recreational opportunities in addition to its vital water supply function, serving as a hub for water resource and climate enthusiasts in the area.

As a key water resource in the region, Lake Williams serves as a critical infrastructure for water supply and recreational activities. With its historical significance dating back over a century, the reservoir continues to play a crucial role in the community. However, ongoing maintenance and monitoring are essential to address safety concerns and ensure the sustainable management of this valuable resource in the face of changing climate patterns and increasing water demands.