Lake Wairarapa's status as a sick lake has been confirmed by a report on the water quality of New Zealand's lakes.
The National Institute of Water and Atmospheric Research report monitored water quality in 113 New Zealand lakes between 2005 and 2009.
The report listed Lake Wairarapa as having a "trophic index"
level of 5.0 in 2009, down from 5.3 in 2006.
Greater Wellington Regional Council freshwater scientist Alton Perrie, who took the measurements, said the trophic scale took into account key nutrient levels, algae growth levels and water clarity. The report listed Lake Wairarapa as "supertrophic", indicating it held an elevated concentration of nutrients.
Sewage was discharged into it, and it was at the bottom of a big agricultural catchment area, neither being good for water quality. Further study of the figures would be needed before precise claims could be made, but Mr Perrie was not convinced of any improving trend in water quality.
South Wairarapa District Council member Mike Gray said the focus needed to include all Wairarapa waterways: "Whichever way you look at it, all our natural water sources need to be protected. We haven't done a good job of it."
He hoped the report findings would spur more action to fix the lake.
Wairarapa Moana Wetlands Park Group chairwoman Fran Wilde said the lake's shocking state was well known.
Environment Minister Nick Smith said: "It is unacceptable that 32 per cent of our monitored lakes have poor water quality and that more lakes are deteriorating in water quality than are improving."
