KEY POINTS:
The state of one of New Zealand's largest lakes is not as critical as feared, but its world-class trout fishing now appears a distant memory.
Lake Ellesmere (Te Waihora), about 20km south of Christchurch, is the fifth-largest lake in the country, and among a group of other large lakes such as Taupo where water quality is a major concern.
Strong comments by Environment Court judge Jeff Smith two years ago led to news reports that Lake Ellesmere was biologically dead.
Judge Smith found the lake was full of nutrients to the point where animal life was not sustainable, and had become green in colour.
Fish and Game said the lake had gone from having trout fishing "unparalleled" anywhere in the world, with 50,000 fishermen visiting a year in the 1970s, to only a few thousand now.
The state of the seaside lake prompted calls from environmental groups for urgent action and sparked new scientific studies.
This week the result of those studies are being presented at a special symposium at Canterbury's Lincoln University. Professor Ken Hughey, who chairs the conference organising committee, said the findings of the various studies conducted in the past two years showed that Lake Ellesmere was far from dead.
"In many parts it is quite healthy," Professor Hughey said. "The one bit that may be terminally ill is the trout fishery.
"The birdlife in the main is doing really well. There are more native bird species recorded at Lake Ellesmere than any other habitat in New Zealand."
The prolonged period of dry summers in Canterbury and the growing demand for water for irrigation had affected water flows into the lake.
Fish and Game said the reasons for the huge decline in the fishery at Lake Ellesmere were not fully understood, but dwindling rivers flows into the lake were a factor.
Environment officer Jason Holland said the number of fish caught in a trap in the river feeding the lake had fallen from 12,000 to 265.
"It won't be able to recover if the water quantity and quality issues aren't dealt with," he said.
Fish and Game is proposing a restocking programme, where brown trout will be released into the lake "just to see what happens".
Options for augmenting flows into the lake will be discussed at the symposium, but any such option is likely to cost millions of dollars.
Professor Hughey said: "We need to do what we can in a cost-effective way to maintain and enhance those values that make Lake Ellesmere such an important wetland."
