Lake Surprise is a reservoir made by Surprise Lake Dam on the Blue Brook in Watchung Reservation. On the border of Berkeley Heights and Mountainside in Union County, New Jersey, the lake was created in 1845 for David Felt's papermill. Previously known as Feltville Lake, renamed Ackerman Lake, renamed Silver Lake, until the Union County Park Commission bought the property for inclusion in the Watchung Reservation naming it Lake Surprise due to the winding road park planners paved, on which a visitor's view of the lake is obscured until the visitor is right next to the lake.