History: Te Waihora Lake Ellesmere was once an estuary of the Waimakariri River and twice its present size; bounding Tai Tapu with extensive wetlands giving way to forests of kahikatea, red beech, matai and totara leading to present day Christchurch. Te Waihora, meaning ‘water spread out’ has been home to Maori for 20 generations. The principal settlement was at Taumutu where the local runanga is still based today. The lake was revered as the most bountiful site in the South Island (Te Wai Pounamu) for resources (mahinga kai) and was referred to as ‘Te Kete Ika Raikaihautu’ or ‘the fish basket of Raikaihautu’. The lake bed was vested in the Ngai Tahu tribe as part of the settlement of its Treaty of Waitangi claim. The European name comes from the Earl of Ellesmere, a member of the Canterbury Association which supported development of the lake. The forests of Banks Peninsula were felled for timber and transported via the lake from the mill at Little River to Timberyard Point on its western shore. Commercial fishing for flounder began in 1864 with up to 250 men employed on the lake and commercial eel fishing began in the 1960’s.
Ecology: Te Waihora Lake Ellesmere is one of New Zealand’s most important wetland systems. It is a brackish, shallow lagoon with an average depth of 1.4m. Covering around 20,000 hectares, it is New Zealand’s fifth largest lake and is internationally significant for its wildlife abundance and diversity. The lake is neither entirely freshwater nor estuarine, it is in fact an Intermittently Closed and Open Lake and Lagoon (ICOLL). Periodic artificial opening of thelake allows for the inflow of sea water and migration of species and increases the diversity of life. The lake was once bounded by extensive wetlands of raupo, flax and sedges of which 81% have been lost or extensively modified. These would have given way to forests of kahikatea, red beech, matai and totara which would have led to present-day Christchurch. Extensive canopies of floating weed beds also provided habitat, food and trapped sediment, creating clear freshwater zones.
Hydrology: The lake’s catchment drains 276,000 hectares, and reaches from the foothills of the Southern Alps, to the Rakaia river, the hills of Banks Peninsula and the plains in between. About three quarters of the catchment is made up of the Central Canterbury Plains. Over 40 streams and rivers feed the lake, some rising as springs within a few kilometres of the lake. Springs supply up to two-thirds of the fresh water that flows into the lake. Water flowing as streams and groundwater may travel over 70km across the Canterbury Plains. By the time it reaches the lake, the water carries many pollutants.
The majority of the surface water comes from the rainfall in the foothills. Rainfall on the plains feeds the extensive groundwater aquifers. Te Waihora is at the bottom of the catchment and is therefore a nutrient and sediment trap. The lake wetlands acted as a nutrient and sediment filter and played an important role in maintaining water quality. Human-induced change in the catchment, intensive farming, and clearing of wetlands have hastened the progression to a high nutrient / high sediment inflow and low flush / low water quality system.
This decline has been amplified by the loss of the lake weed beds which held clear fresh water zones at the mouths of the streams and reduced turbulence and sediment disturbance. These beds were lost in the Wahine storm of 1968. The lake is now classified as highly eutrophic, but the shallowness of the lake and its exposure to wind keep the waters oxygenated and save it from regular toxic algal blooms.
Lake Issues and Management: A national Water Conservation Order was issued in 1990 in recognition of Te Waihora/Lake Ellesmere’s contribution to outstanding amenity or intrinsic values. This was amended in 2011 to recognise further values that warranted protection and the height of the water in the Lake is managed especially to protect these values: habitat for wildlife, indigenous wetland vegetation and fish; and its significance in accordance with tikanga Māori in respect of Ngāi Tahu history, mahinga kai and customary fisheries.
The lake is subjected to lower inflows from its tributaries due to lower land surface recharge across the plains and increased groundwater extractions. As a result there is a Joint Management Plan between the Department of Conservation and Te Runanga o Ngai Tahu which aims for integrated management of the natural and historic resources in the plan area, for mahinga kai and conservation purposes.The Canterbury Regional Council is responsible for water-quality monitoring in the lake and tributaries, pest management, and maintaining a system of drains in the Halswell Drainage District. The Selwyn District and the Christchurch City Councils manage networks of drains and lakeside recreation reserves and are responsible for the protection of natural resources in their districts.
Lake opening:The lake today covers about half its historic level and averages about 1.2m. The level is managed by periodically opening the lake to the sea. The lake is opened mechanically approximately three times a year to manage for a range of values, including wildlife, wetland vegetation and fish habitat, mahinga kai, customary fisheries, water quality, summer levels, land inundation, waterway networks and infrastructure, and fish migration for a variety of species in Autumn and Spring.
Recreation:The lake enables a range of recreational activities, including walking, bird watching, photography, water sports, cycling, fishing, gamebird shooting….and geocaching. It is internationally renowned for its birdlife, with around 170 different species recorded. Information about the birdlife can be found at New Zealand Birds Online. Information about fishing and gamebird shooting can be found at the Fish & Game websiteand the shooting season opens on the first Saturday in May each year.
To log this Earthcache: you will need to complete the following task. Please email your answer, but DO NOT post it with your online log. Once you have emailed your answer, you may go ahead and post your online log. No need to wait for a reply.
Drawing on your observations of the lake and the main text; describe the physical condition of the lake at the time of your visit and how this might be influenced by the situation elsewhere in the catchment.
In particular think about the average depth of the lake, its overall size and what happens to all the water and its contents that flows into the lake and where it can go to. If the lake has no outlet where else might water go, especially in the hot, summer months?
What do you think the quality of the water might be, and what will impact on that quality? What would be the impact on the water quality if the lake is not opened to the sea on a regular basis?
(Optional) If you want to find out more about the lake levels, look up the WET website (http://www.wet.org.nz) and publish the lake level with your log so it builds a set of data for other geocachers to study.
(Optional) Take a picture of the lake with a time stamp. You are welcome to include yourself in the picture.
Acknowledgements: Information for this Earthcache was derived from the Waihora Ellesmere Trust (WET) website (http://www.wet.org.nz). WET’s permission to use their images is gratefully acknowledged. WET is a community organisation dedicated to the improvement of the health and biodiversity of Te Waihora Lake Ellesmere and its catchment. It was formed in 2003 following two years of extensive community involvement. More information, including how to become a member, can be found at www.wet.org.nz.
Congratulations to mrdan01 for a swift and very comprehensive FTF response that sets a high bar for others. Thanks also to Hamish Rennie, Lincoln University and GeoAwareANZ2 for peer review of the content and to Kiwi Moose for the initial idea. All very much appreciated.