Sherwood Dam, known also as Lake Sherwood Dam, Alturas Dam, and Potrero Dam, is a concrete arch dam in the Santa Monica Mountains near Thousand Oaks, California. Completed in 1904, its construction led to the creation of the Potrero Lake (since renamed Lake Sherwood) over the following winter. It was the first reservoir of its size in the area, and remains one of the oldest standing dams in California.