Lake Forsyth (known to

Māori Māori or Maori can refer to: Relating to the Māori people * Māori people of New Zealand, or members of that group * Māori language, the language of the Māori people of New Zealand * Māori culture * Cook Islanders, the Māori people of the C ...

as Te Roto o Wairewa) is a lake on the south-western side of Banks Peninsula in the

Canterbury Canterbury (, ) is a cathedral city and UNESCO World Heritage Site, situated in the heart of the City of Canterbury local government district of Kent, England. It lies on the River Stour. The Archbishop of Canterbury is the primate of ...

region of

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

, near the eastern end of the much larger Lake Ellesmere / Te Waihora. State Highway 75 to Akaroa and the Little River Rail Trail run along the north-western side of the lake. The lake is fed by the Takiritawai River. Its natural discharge into the sea is through a gravel bank at the small community of Birdlings Flat. Wairewa was an important source of eels as food for the

Ngāi Tahu Ngāi Tahu, or Kāi Tahu, is the principal Māori (tribe) of the South Island. Its (tribal area) is the largest in New Zealand, and extends from the White Bluffs / Te Parinui o Whiti (southeast of Blenheim), Mount Mahanga and Kahurangi Point ...

tribe (indigenous Maori people of the South Island). It is the only Ngāi Tahu customary lake. The Wairewa Rūnanga, one of 18

rūnanga In Tikanga Māori (Māori culture or practice), a (runaka in Southern Māori dialect) is a tribal council, assembly, board or boardroom. The term can also be a verb meaning "to discuss in an assembly". An iwi (tribe) can have one governing rūna ...

of Ngāi Tahu, are the guardians or kaitiaki of the lake. Deforestation of the surrounding hills has led to erosion and silting up of the lake. The lake is

hypertrophic Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It is distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number.Updated by Linda J. ...

, leading to

eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...

with corresponding poor water quality. This decline in water quality has been known since the early 1900s. In 2016, after a spell of dry weather, the water quality deteriorated and recurring

algal bloom An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term ''algae'' encompass ...

s made the water toxic. Animals, including pets and sheep, died after drinking the water. The Wairewa Rūnanga has created an outlet canal that is occasionally opened to the sea when there is a risk of flooding due to heavy rain. The lake's health has improved since the canal was created. A bridge over the canal was built in 2018. Prior to that, vehicle access across the outlet was restricted for up to weeks at a time whenever the outlet canal was opened to the sea.

Geography

Lake Forsyth is long, narrow and shallow. It has undergone dynamic change over its short lifespan, from bay to

estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') ...

. Up until a few thousand years ago it was an embayment in the

Canterbury Bight The Canterbury Bight is a large bight on the eastern side of New Zealand's South Island. The bight runs for approximately from the southern end of Banks Peninsula to the settlement of Timaru and faces southeast, exposing it to high-energy storm w ...

, fully exposed to the fury of southerly waves. Over time, a spit of sand and gravel grew, fed by a strong longshore drift. The spit, grew steadily, until it ran into Banks Peninsula and could grow no more, but the sand and sediment kept coming. The spit had become a barrier, now named Kaitorete Spit. It closed off a nearby lake basin from the sea, creating the waituna now known as Lake Ellesmere / Te Waihora. Within perhaps a further 1000 years, the barrier barred the mouth of the bay turning it into an estuary, where tidal waters could still go in and out. However, the progressive thickening of barrier impounded the estuary, kept the sea out, and it became a lagoon. Freshwater seeped out but sea water couldn’t flow it. The opening was navigable by

waka Waka may refer to: Culture and language * Waka (canoe), a Polynesian word for canoe; especially, canoes of the Māori of New Zealand ** Waka ama, a Polynesian outrigger canoe ** Waka hourua, a Polynesian ocean-going canoe ** Waka taua, a Māori w ...

canoes and small coastal schooners in the 1860s. If natural coastal processes were left to operate, Lake Forsyth would eventually become a lake. It is one of many lagoons and estuaries misnamed on New Zealand maps.

References

External links

{{Commons category, Lake Forsyth
Wairewa Research Project
– a collaborative project by the Wairewa runanga focussing on rehabilitation of Te Roto o Wairewa/Lake Forsyth Forsyth Geography of Christchurch Lagoons of New Zealand