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|Lake Forsyth |
|Location||Canterbury, South Island|
|Primary inflows||Takiritawai River|
|Primary outflows||seepage, artificial opening|
|Basin countries||New Zealand|
|Max. length||7.6 km (4.7 mi)|
|Max. width||1 km (0.62 mi)|
|Surface area||627.5526 ha (1,550.716 acres)|
|Average depth||1 m (3 ft 3 in)|
|Surface elevation||0 m (0 ft)|
Wairewa was an important for providing tuna [eel]s as food for the Ngai Tahu tribe (indigenous Maori people of South Island). It is the only Ngai Tahu customary lake. Wairewa Runanga one of the 18 Ngai Tahu Runanga are the guardians or kaitiaki of the lake. However deforestation of the surrounding hills has led to erosion and silting up of the lake.
The lake is hypertrophic, leading to eutrophication with corresponding poor water quality. This decline in water quality has been known since the early 1900s. So far, attempts of opening up the lake to the ocean to rectify the problem have had limited success. In 2016, after a spell of dry weather, the water quality deteriorated and recurring algal blooms made the water toxic. Animals, including pets and sheep, died after drinking the water.