Walled Lake lies in the headwaters of the Middle One Branch of the Rouge River watershed and drains 4 square miles toward the Detroit River. The Rouge River drains 438 square miles across 48 municipalities and three counties, is home to 1.5 million people, and discharges to the Detroit River near the Rouge Assembly Plant in Detroit. A major threat to this watershed is nonpoint source pollution from stormwater runoff, which carries contaminants such as fertilizer, oil, grease, toxic chemicals, sediment, salt, and bacteria into waterways; Walled Lake has 36 stormwater outfalls that send runoff directly into the lake, and both Walled Lake and Novi are under a Phase II Stormwater Permit from the United States Environmental Protection Agency requiring action to reduce and mitigate runoff impacts. The lake probably formed about 12,000 years ago as a natural kettle lake when glacial ice created a depression in outwash that filled with meltwater; it is primarily spring-fed, also receives water from several small creeks, and drains by an outlet to the Middle Branch of the Rouge River. Walled Lake took its name from a long stone wall along the west shore, first described in 1826 by settler Walter Hewitt as about 150 feet long, 4 feet high, and 5 feet wide, though its origin remains unknown, with explanations ranging from Native American fish trapping and a memorial to a drowned fisherman to drift deposits from water and ice action or glacial activity. Milestones in the area's history include a Potawatomi camp along the western shore before 1824 near the Grand Indian Trail, Hewitt's log cabin in 1825, the White Rock Indian Trading Post in 1830, the platting of the village in 1836, the arrival of Dr. James M. Hoyt in 1840, the building of Stonecrest Schoolhouse in 1860, railroad service beginning in 1883, the opening of Walled Lake Park in 1929, the destruction of Casino Shores Pavilion by fire in 1965, sewer installation by Walled Lake and Novi in 1979 followed by improved water quality within five years, and Walled Lake joining the Main Street Oakland County Program in 2000 to build and promote its downtown.