Lake Hayes residents are being warned possible solutions to the lake's algal bloom problem could be costly, with no guarantee of success.
Over the past 40 years, the lake has had increasing high levels of nutrients and in the past three years experienced algal blooms which have given it an unsightly brown appearance.
A recent report to the Otago Regional Council environmental science committee outlined the issue and possible solutions.
Environmental information and science director John Threlfall said council representatives had met the Lake Hayes Water Quality Enhancement Society in January to go over the issues.
Council monitoring had found that while nutrient input levels from Mill Creek to the lake were improving, significant changes to the lake quality in the short term were unlikely, due to historical land-use practices and intense phosphorous loading in the lake sediments.
Committee chairwoman Gretchen Robertson said any improvements could prove very costly, with one option alone, capping the sediment, estimated to cost $1 million, while another, the SolarBee, $700,000.
Cr Duncan Butcher said it was an issue which had been around for decades and the council had been monitoring the lake, but it came down to cost, who would pay and whether or not the suggested treatments would be successful.
The option of siphoning water from the depths of the lake was seen by some people as a "simple fix" which would not cost too much, but he questioned that.
Mr Threlfall said there were issues with the siphoning process such as the effect changing the height of the lake would have on the Kawarau River and the environmental effects of discharging the lake water.
"We don't believe any of these individual options are necessarily the answer and with the costs associated there is no cost benefit."
If the community wanted to pursue the options further it could do so through the Long Term Council Community Plan consultation process, he said.
The council was providing what information it could to the group and continuing a collaboration with University of Otago into researching possible causes of the problem, he said.
Cr Stephen Woodhead said the algal bloom did not change the look of the lake too much and might just be "one of those seasonal things you put up with".
Mr Threlfall said, except for possible skin irritation, there were no other known health issues associated with swimming in the lake.
