Grovetown lagoon is one of the few natural wetlands remaining on the Wairau plains in Marlborough. Geographically speaking the lagoon is an ‘oxbow lake’. This type of lake is formed over time when a river creates a curving, meandering path which eventually nearly cuts back onto itself. (See aerial image). As the ‘neck’ of the meander becomes narrower and narrower it becomes susceptible to breaching during the next major flood, which in this case occurred in 1861. The high waters and fast flows broke through the narrow piece of land which in effect straightened the river’s path leaving an isolated curved lake where the river once flowed.
As the Wairau river continued on its new, straighter path, the Grovetown oxbow lake’s water remained clear and fresh, even in times of drought, due to the numerous nearby freshwater springs flowing into the lagoon. Fish and eels continued to thrive in the wetland while birds made their homes around the sheltered water using it for feeding, nesting and raising their young.
Unfortunately, as time went on, willows and invasive climbing vines overcame the banks of the lagoon. Adding to the environment degradation, effluent and silt from farming practices and the local Grovetown residential settlement began to pollute the waters of the loop.