Hempstead Lake State Park, now popular among anglers and home to the largest freshwater lake in Nassau County, emerged from a long transformation driven by Brooklyn's need for water. In 1851, the Brooklyn Water Works Company, seeking to meet the demands of a rising population, found Mill River's streams to be the most robust in the area, and water mills operated there until the 1870s. The company then bought the whole valley to build the Hempstead Storage Reservoir, spending $1.4 million, but engineers discovered that water seeped into the porous sand below. Brooklyn eventually turned to the Catskills for its water supply, and in 1925, with the building of Southern State Parkway, the reservoir officially became Hempstead Lake State Park. As of August 2010, most of the standing building had been demolished, and by 2019, nothing remained of the structure.