The lake sits within the Kaikohe-Bay of Islands volcanic field. The lake was formed when an ancient lava flow blocked a valley, forming the northern shoreline. It is five km in length and covers 12.3 km², however it is only 2.6 metres deep (and as low as 1.5 m during summer). The lake has few inflow streams, mostly in the southern part of the lake. The Utakura River (south-western margin) is the main outflow which goes to the Hokianga Harbour. The lake catchment is predominantly pasture, with a few areas of native scrub and mature bush.