Lake Tappan is a reservoir impounded by the Tappan Dam on the Hackensack River, straddling the border between the U.S. states of New Jersey and New York.[2]:221–223 Within New Jersey, the lake traverses the border separating the municipalities of River Vale and Old Tappan in Bergen County, while extending northward across the New York state line into the town of Orangetown in Rockand County. The reservoir was formed in 1967, flooding areas that included the former CAPROC Field Civil Air Patrol airstrip.[3]