Wairarapa is home to one of New Zealand’s dirtiest lakes which a scientist has revealed will take a century, maybe longer, to clean up to any great extent.
The shallow Lake Wairarapa has suffered decades of abuse, with sewage and effluent entering the rivers that feed into it.
Now, councils and groups are working together to try to cut nutrients and pollution levels, knowing the lake is never likely to return to its former pristine glory.
This challenge is coupled with a timeframe that is longer than the average New Zealander’s life expectancy.
While experts say the damage has been done, a Maori iwi representative hopes changes of the water quality could be seen in half the predicted time.
But the chairman of Greater Wellington Regional Council, Chris Laidlaw, says the public perception of who is at fault needs to change.
Wairarapa Moana is the largest lake and wetland complex in the lower North Island.
The lake is a shallow, 2.5m at the deepest point, and suffers from two layers of sediment which causes some of the biggest issues with water quality.
More than a century of development, including drainage and flood control schemes, has left the lake in a “highly modified state”, a report presented to the Greater Wellington Regional Council Environment Committee last week said.
The lake is classified as ‘supertrophic’, meaning it has very high levels of nutrients, classing it as very poor water quality by Land Air Water Aotearoa.
This is the last trophic level before a lake is ‘dead’.
In comparison, Lake Taupo is classified as ‘oligotrophic’, meaning it has good water quality.
The Ruamahanga River used to flow directly into Lake Wairarapa, but was diverted from it in the 1970s, so Lake Wairarapa now receives less than 10 percent of the water that used to flow through.
Agriculture has also intensified over the past decades meaning more stock effluent and fertiliser run-off is affecting the lake.
Lake Onoke and its surrounding wetlands also have problems with water quality.
Regional council senior science co-ordinator Penny Fairbrother said one of the worst things that has been done is the draining and ripping out of the surrounding wetlands.
“We have essentially ripped out the kidneys of the land and that is very prominent around Lake Wairarapa,” she said.
Kahungunu ki Wairarapa environment manager Ra Smith said the lake’s water quality could take 100 years to improve, but he hopes the work being done will shorten that prediction.
“We won’t be sitting on our hands and saying why is nothing happening,” he said.
“I would hope that in 50 years we would be seeing something different.”
There are a handful of ongoing research projects led by the Wairarapa Moana Wetlands group that could offer more options of improvements at Lake Wairarapa.
Possible core mud sample testing, and the planting of manuka to see if the roots could filter nutrients, are just two of several projects that the group has taken on.
Mr Smith is hoping the core mud samples would tell him what is in the sediment.
The initiatives taken on by the council were also contributing to the lake’s progress, but it was more about the positive attitudes to help with the change that was the “good thing”, he said.
Wairarapa Moana is in the final stages of gaining Ramsar status, an international recognition of wetlands.
If they receive the status, it will open up more research funding opportunities for them, he said.
Regional Council chairman Chris Laidlaw said the public perception is that farming is to blame, but “it’s not just farming”.
“We are all guilty and people need to take responsibility,” Mr Laidlaw said.
“The lake has been compromised by decades of mismanagement.”
This is a practice that is going to take decades to flush out the contamination.
What is the regional council doing?
Greater Wellington Regional Council restricts the direct discharge of animal effluent, waste water and other types of pollutants into Wairarapa’s rivers and streams.
The main point of contaminants in the Ruamahanga River comes from Wairarapa towns’ wastewater treatment plants, the report said.
The regional council Farm and Environment Plan (FEP) Programme encourages farmers to be aware of how farming practices can affect the wider catchment area and water quality.
It focuses on intensively farmed land such as the area around Lake Wairarapa.
The council provides financial incentives for on-ground works such as fencing and riparian planting.
Research suggests that it can reduce land sediment loss by up to 70 per cent.
The proposed Natural Resources Plan sets the objectives for the use of the region’s natural and physical resource.
Of interest to the Ruamahanga catchment is the proposed introduction of stock exclusion to cut the amount of run-off into the lake.