"The NID [National Inventory of Dams] consists of dams meeting at least one of the following criteria: 1) High hazard classification - loss of one human life is likely if the dam fails; 2) Significant hazard classification - possible loss of human life and likely significant property or environmental destruction; 3) Equal or exceed 25 feet in height and exceed 15 acre-feet in storage; and/or 4) Equal or exceed 50 acre-feet storage and exceed 6 feet in height. The goal of the NID is to include all dams in the United States that meet these criteria, yet in reality, is limited to information that can be gathered and properly interpreted with the given funding. The NID initially consisted of approximately 45,000 dams, which were gathered from extensive record searches and some feature extraction from aerial imagery. Since continued and methodical updates have been conducted, data collection has been focused on the most reliable data sources, which are the many federal and state government dam construction and regulation offices. In most cases, dams within the NID criteria are regulated (construction permit, inspection, and/or enforcement) by federal or state agencies, who have basic information on the dams within their jurisdiction. "