Lake Wairarapa lies at the southern end of the Wairarapa Plains, which are formed in the fault angle of the West Wairarapa Fault. It has an area of 31 square miles and is fed by the large Ruamahanga (1,300 square miles) drainage and Tauherenikau (catchment, 80 square miles) Rivers. The lake is very shallow, probably not more than 10 ft deep, with gently sloping margins. The shore is ill defined, with many areas of swamp and partly isolated lakelets, particularly round its south-eastern margin. Its entire drainage flows through the Lower Ruamahanga River to Lake Onoke, which is a bar-dammed lagoon on the shore of Palliser Bay.
Lake Wairarapa was formed by alluviation across an extensive arm of the sea following the rise of sea level after the melting of the glaciers of the last Ice Age some 5,000–10,000 years ago.
Lake Wairarapa is known for its excellent duck shooting, providing ideal conditions for ducks in its shallow waters and swampy margins. Some yachting is also done. The lake provides an enormous ponding area for flood waters. The highest flood recorded reached 10 ft above normal lake level in 1880.
The generally accepted meaning of Wairarapa is “glistening waters”, though its origin is obscure. It is said that when Hau, a legendary traveller, saw the beautiful lake and valley, his eyes glistened with delight.
by Thomas Ludovic Grant-Taylor, M.SC., New Zealand Geological Survey, Lower Hutt.