In NJ there are no dams that are totally private and require no inspection as long as the spillway exits to a waterway. The classifications for dams are 1,2,and 3. What you are describing is a class 3 dam with a lake volume that would not exceed the capability of the stream to carry should it be breached. Under the NJDEP regulations, your dam only requires a (yearly?) visual inspection by a civil engineer and an O&M Plan that must be submitted to the NJDEP. If the pond/lake is bounded by another property owner or if there is a volume in the pond that exceeds the capability of the stream should it breach, you then must have all the same including an inspection performed by a qualified dam inspector. Contact the New Jerser Dept. of Environmental Protection, Dam Safety Div. Mr.Dewey Lima at would be a good starting point.