Technically the term “dam” relates to the barrier constructed across a stream, valley or similar natural depression for the purpose of impounding water, but popular usage includes the impounded water along with the barrier.

Apart from the obvious requirements of storage for community or stock water supply, the economic purposes served by impounding of water by dams are: land irrigation, generation of electricity by hydraulic power, amelioration of flooding by partial retention of flood waters, and improvement of natural waterway facilities for inland navigation. Of these, only the first two have been exploited to any extent in New Zealand. Some details of the more important dams are tabulated.