There are a number of technical and legal definitions of a dam, but generally it is any structure that impounds or diverts water. In New Jersey, a dam is defined as any artificial dike, levee or other barrier, together with appurtenant works, which is constructed for the purpose of impounding water on a permanent or temporary basis, that raises the water level five feet or more above the usual, mean, low water height when measured from the downstream toe-of-dam to the emergency spillway crest or, in the absence of an emergency spillway, the top-of-dam.
New Jersey Dams 