Opening Te Waihora/Lake Ellesmere
Te Waihora/Lake Ellesmere Level Information
The lake is currently OPEN to the sea. The calm average level of the lake as recorded on Tuesday 25th July was 1.60m. The next update will be sent out on Monday 31st July.
Staff and contractors are on site and have opened the lake at 7am 25 July 2017. Heavy equipment will remain on standby in case the cut re-closes, particularly at the next high tide at 6pm 25th July. A reduction in lake level will be noticeable over the next couple of days.
Q: What was the lake level reading before this one?
A: 1.55m, calm average level, Monday 25th July 2017
Q: When was the lake last opened to the sea?
A: The lake was last opened on 3rd July 2017 and closed naturally on 14th July 2017. The lake was open for 11 days.
Q: At what levels can the lake be opened to the sea at this time of year?
A: From 1st April until 31st July the minimum level the lake may be opened is 1.13m. From 1st August until 31st May the minimum level the lake may be opened is 1.05m.
Te Waihora/Lake Ellesmere is the largest lake in 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/Lake Ellesmere's opening is governed by a National Water Conservation Order and a range of resource consents held jointly by Te Rūnanga o Ngāi Tahu and Environment Canterbury. However, many groups have an opportunity to air their views before a final decision is made.
Openings tend to be aligned with fish migration periods and other habitat values of the lake. Tuna (freshwater eels) come in from April to June via kōumu/drains or a full opening. Pātiki/flounder, inānga/whitebait, sea-run trout and other species enter the lake around September and October.
Factors to take into account include:
- access for traditional mahinga kai including gathering of swan's eggs
- avoiding low lake levels in summer and desiccation of wetland margins
- the need for variation in lake levels to support complex and diverse wetland bird and plant habitats
- managing land inundation (including from wind effects)
- the effects of high lake levels on drain networks and infrastructure.
Experts provide technical advice around the machinery. The weather and sea conditions are forecast while lake levels are monitored. It generally takes three to seven days to forge the opening but if sea conditions are rough, past experience has shown it could take up to six weeks.
Historical methods for opening the lake have included horse-drawn scoops and two outlet culverts in the early part of the 20th century — Dobson’s Culvert and Pannett’s Culvert. Heavy machinery has been used since the 1930s. For more details, read these accounts.
Once the lake is opened, there is limited ability to control how long it stays that way. The length is determined by weather and sea conditions, and how quickly gravel is deposited by the sea to close the cut.
Artificial closure has not been attempted to date however the water order allows for the lake to be artificially closed when it reaches 0.6 metres above sea level between 1 October and 31 March. Such a closure would only be considered in summer if lake levels were very low and sea conditions were too calm to create natural closure.
We monitor effects of the lake opening including:
- keeping an eye on channels through the spit from the lake edge to assist tuna/freshwater eel migration
- sediment sampling and experimental dredging of the deeper channels of the lake bed to work out whether this will result in greater flushing to improve water quality and associated wildlife and mahinga kai values
- investigating the feasibility of opening the lake at the southern end of Te Korua near the mouth of the Waikekewai Creek and the conditions needed in the lake to make a successful opening in this area (Te Korua was the traditional opening site used by Ngāi Tahu)
- Investigating the feasibility of establishing a controlled outlet from Te Waihora/Lake Ellesmere to the sea.