Opening Te Waihora/Lake Ellesmere
Te Waihora/Lake Ellesmere is the largest lake in Waitaha/Canterbury and has no natural outlet to the sea. It is valued for cultural and environmental reasons and was opened by generations of Ngāi Tahu before Pākehā arrival. The first written settler's record of an artificial opening between the lake and sea was in 1852. It has been opened over 300 times since.
Te Waihora water level information
Current state: Te Waihora is currently OPEN to the sea. Due to high winds, an accurate lake level as at 8am on Monday, 17 November could not be obtained. The next regular update will be on Monday, 24 November 2025.
Previous reading: The wind affected average lake level on Monday, 10 November was 0.60m.
Previous opening: The lake was mechanically opened on 9 October 2025.
Minimum opening levels: From 1 August to 31 March, the lake can be opened at 1.05m.
24/7 access to Te Waihora water levels: Average readings are taken from gauges at Taumutu and Seabridge Road/Nutts Cut. Wind effects are not included in the data but can be requested from our advisory team. View lake level data.
How the decision to open the lake is made
Te Waihora's opening is governed by a National Water Conservation Order (NWCO), Te Waihora Te Rūnanga o Ngāi Tahu and us.
A protocol group, made up of several organisations representing different interests and values, provides advice on the potential opening of Te Waihora, with the final decision sitting with Te Rūnanga o Ngāi Tahu and us.
The parties involved in the decision-making process include:
- Te Taumutu Rūnanga
- The Department of Conservation
- Lake Ellesmere/Te Waihora Rating District Liaison Committee
- North Canterbury Fish and Game Council
- Lake Ellesmere commercial fishermen
- Selwyn District Council
- Christchurch City Council
- Waihora Ellesmere Trust
National Water Conservation Order
The National Water Conservation Order (NWCO) sets the minimum opening levels at which artificial openings to the sea can be considered, as well as levels under which the lake can be artificially closed from the sea.
The consent conditions require the decision-makers to consider a suite of matters, including:
- the outstanding amenity or intrinsic values which warrant protection, including habitat for wildlife, indigenous wetland vegetation and fish
- significance under tikanga Māori in respect of Ngāi Tahu history, mahinga kai and customary fisheries, including fish passage
- operational and infrastructure considerations like summer lake levels, managing land inundation, tuna/eel migration and other fish passage and effects on drainage networks and infrastructure.
Opening Te Waihora to the sea
Once the decision has been made to open the lake, our rivers team engages contractors to undertake the work.
It usually takes three to seven days for an opening attempt to be made, but if sea conditions are rough or gravel build-up since the last opening is significant, it can take weeks.
Steps involved in opening the lake:
- Creating the pilot channel: Heavy earthmoving machinery, including bulldozers and excavators, creates a pilot channel through Kaitorete Spit near Taumutu that is typically 15 metres wide and 1.8 metres deep.
- Channel length: Depending on the volume of shingle overwash into the lake at the time, the pilot channel can vary from 100 metres to over 300 metres in length.
- Natural widening and migration: After making the final cut to the sea, the opening is left to further widen naturally, and the mouth of the channel may erode to more than 100 metres wide, and migrate along the beach in response to wind direction and tides.
Costs of opening the lake
The cost of each opening is dependent on site conditions, including:
- the amount of gravel deposited on the beach
- swell size and orientation and coastal conditions
- and if multiple attempts are required to achieve a successful opening.
An opening is considered “successful” when it has survived long enough to allow the lake level to drop significantly below the minimum opening level.
Costs of opening can vary from $50,000 to over $200,000, depending on the amount of work required. The operation is funded through targeted, works and services, and general rates, as well as Central Plains Water Trust contributions.
Challenges with alternative lake opening options
Many alternative options for opening Te Waihora/Lake Ellesmere to the sea (including permanent infrastructure) have been investigated and proven to be impractical, impossible or too expensive to construct and maintain. These include:
- culverts/weirs/syphons
- diversions (the lake outfall to the Rakaia River mouth; via the Huritini/Halswell River to the Ihutai/Avon-Heathcote Estuary; via a canal to Wairewa/Lake Forsyth
- a breakwater to protect the opening.
Lake level management: For more information on lake level management at Te Waihora, visit the co-governance group website.