Known in Maori as Te Waihora (the spreading water), this shallow lake of many moods can cover 30,000 hectares of coastal lowland when in full flood. In prehistoric times when it got that large, it would burst out through the sand and gravel spit separating it from the sea.

Beginning in Maori times and continuing through to the present day, the lake's level has been artificially regulated by cutting a channel to the sea several times a year. This keeps its area at around 19,000 hectares, making it still New Zealand's largest coastal lake and the fourth largest lake overall.

The lake, once capable of depths of up to five metres, is now kept at an average depth of two metres. The regular openings prevent flooding and also maintain fish stocks by allowing ocean-spawning fish (e.g. eels, mullet, flounder) to enter and leave the lake.

Photo of lake ellesmereA few commercial fishers work the lake for eels, flounder and 'herrings' (yellow-eyed mullet) while recreational users find it ideal for sailing, kayaking, motor boats, wind-surfing, water-skiing, jet-skiing, duck shooting, picnicking, photography, bird-watching or just contemplating to the rhythm of the gently lapping water.

The lake's iconic black swans once numbered up to 80,000, but their numbers fell dramatically after the Wahine storm of 1968 which ripped out their main food supply, the profuse weed-beds that grew on the shallow lake bottom. Some swans are still here but neither the weed nor they recovered their former abundance.

The eel population, too, once legendary for its size, is now smaller, partly through over-fishing in the 1970s-80s and partly through changes in the lake's vegetation and ecology. The lake has been affected by a century of wastewater run-off from farms, streams and townships, as well as several decades of sewage and agrichemical sprays.

Efforts to restore the weed beds, improve the water quality and protect the lake's biodiversity are now underway, with the Department of Conservation (DoC), the regional council (Environment Canterbury), the local Maori tribe (Ngai Tahu) and local volunteers uniting to protect and enhance the lake and its surroundings. To join them, or simply to find out more about Lake Ellesmere, you can visit www.wet.org.nz.

In December 2005, Ngai Tahu and DoC signed up to a joint management plan for the lake which aims to:

...restore Te Waihora as a tribal food resource, to protect the conservation values of the area, and to restore and protect Te Waihora for the use and enjoyment of all New Zealanders, now and in the future...