The Kai Iwi Lakes are basin type dune lakes formed in consolidated sand of late Pleistocene geological origin. They were formed by the accumulation of rainwater in depressions of sand underlain by relatively impermeable ironstone pans. Dune lakes are one of nine major lake types found in New Zealand and are the predominant type found along the west coast of the North Island. Lake Taharoa which covers 237ha is the third largest dune lake in New Zealand. Lake Waikere cover 35ha and Lake Kai Iwi 33ha. Together the three lakes occupy well over half the total area of the domain.
Lake Kai Iwi and Taharoa are connected by a narrow channel and are about 70 metres above sea level. Lake Waikere is more elevated and about 79 metres above sea level. Lakes Taharoa and Waikere are the deepest known dune lakes in the country. The NZ Oceanographic Institute bathymetric chart of lakes record the maximum depth of Lake Taharoa to the 37 metres, and Lake Waikere 30 metres. Lake Kai Iwi is considerably shallower than the other two lakes and has a maximum recorded depth of 16 metres.
View across the Lake
The Kai Iwi Lakes have no known natural inlets or outlets. Their principal source of water is likely to be rain which falls directly onto the lake surface. As a result their levels fluctuate considerably with climatic conditions. Seasonal lake level movements of 400-600 mm have been recorded on Lake Taharoa. Lake water temperatures also vary considerably during the year. Temperatures of 12.8°c to 21.0°c have been recorded. Thermal stratification sometimes occurs during the summer with the formation of distinct water layers of different temperatures.