The Grovetown Lagoon was once part of the Wairau River. Today it is an oxbow lake connected to the river through the northern and southern outlets.
In 1848 there was a large earthquake estimated to be at 7.1 said to be the worst in Maori memory. This was followed by two after shocks, each one close to 6, causing subsidence of the Wairau Plain and changes to the Wairau Estuary and the outlet to the sea.
In May 1861, the land joining Maori Island to the site of the Wairau Pa was broken through. The break was cut through permanently with flooding in 1868, leaving the ox bow now known as Grovetown Lagoon.
With an area of 22 hectares and a catchment of some 12.5 kilometers, the Lagoon is the last of the wetlands once covering the Wairau Plain.
Historically Rangitane, Ngati Rarua and Ngati Toa have used the wetland and the waterways into it as a food resource, gathering water cress and catching tuna, inanga, patiki and koura. There was also an abundance of harakeke and raupo harvested and used traditionally and later on for commercial purposes.
If you are standing at the lookout, looking into the lagoon, the river used to flow to the right. After the Grovetown settlement was constantly being flooded (1860's) by the end constantly silting up, the locals dug out the outlet to the left, to form a rigid path for the natural springs in Grovetown, (and drains flowing into it) to drain back out to the river. There is a pump at each outlet, to allow the water to only come out of the lagoon, and so the river flow cannot come back up.