From the roadside, Lake Wairarapa looks like any other lake — a vast expanse of water surrounded by farmland and bush reserves.

The tarsealed ring road opens up the fanciful possibility of round-the-lake cycling events, and the watery expanse looks ideal for boating, water sports and fishing.

But things are not as idyllic as they might seem. Lake Wairarapa is terminally ill, and just one stage away from becoming extinct. In scientific terms, it is supertrophic — taking its last gasp.

Flood mitigation measures are killing the lake but finding solutions that suit all parties is proving difficult
Flood mitigation measures are killing the lake but finding solutions that suit all parties is proving difficult

How can this be in today's world of environmental awareness and super-science? What in nature has turned this lake from being the dominant natural entity in the whole lower Wairarapa into a sickly shadow?

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The lake liked to flood its wetlands at every opportunity, often covering twice its size after heavy rains. That didn't suit mankind's purposes for the area, and back in the 1960s the then Catchment Board started investigating flood management schemes.

This was grand-scale thinking, with barrage gates to be installed at the lower end of the lake to stop it in its tracks. Also, the Ruamahanga River would be artificially channelled away from the lake, so its contribution could be flushed straight out to sea via the much smaller lower lake, Lake Onoke.

It's a situation that is raising its head across New Zealand — best-thinking flood protection systems from last century that are no longer fit for purpose nor comply with today's environmental demands.

At one time, the talk was of draining Lake Wairarapa completely, says Alastair Smaill, Ruamahanga Whaitua project manager at Greater Wellington Regional Council.

"It was a typical Ministry of Works scheme in the early 60s," says Alastair. "Land development had started and the barrage gates were needed to control the lake levels. It has since provided a lot of economic benefit, but the whole scheme is not to today's standards."

He says everyone accepts that Lake Wairarapa needs help to restore its water quality, but for some it is a case of "as long as it doesn't affect me".

"There is tension between those calling for the restoration of the lake and other users in the lower valley, and their economic interests."

Two iwi groups are at the forefront of efforts to restore the mauri (life-force) of Lake Wairarapa, and they are supported by a range of environmental groups.

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The farmland abutting the lake is in most places being well utilised, and it is clear that generations of farmers have made a positive mark. Any change to lake levels and water-take allocations will impact their livelihood directly.

The lake's former wetlands domain was unbelievably vast, stretching north as far as Greytown on occasion. Now held securely in about 80 square kilometres, it has covered as much as 300 square kilometres. It is now so shallow that the wind stirs up the phosphorus-laden sediment on the bottom, making it very murky.

Clearly, a return to the days before the Lower Valley Drainage Scheme is not an option.

The debate now is all about how the lake can be saved, along with the farmland.

Lake Wairarapa is fed at its northern end by the Tauherenikau River and once used to take in the Ruamahanga River before overflowing into Lake Onoke and out to sea. The drainage scheme changed that by diverting the Ruamahanga away from the lake and by installing the barrage gates to control the lake's outflow.

BARRAGE GATES

Ironically, the installation of the barrage gates helped save the lake from being drained completely.

The barrage gates are dominating the discussion but that's not the single solution. How they are used to control lake levels is the argument.

Some people are calling for the clock to be turned back, with the Ruamahanga once again allowed to enter Lake Wairarapa in the view that this flow would improve the lake's water quality. Some want the barrage gates to be removed as well.

The environmental consents for the barrage gates come up for renewal soon, and this is acting as a catalyst for action.

"The barrage gates are dominating the discussion," says Smaill, "but that's not the single solution. How they are used to control lake levels is the argument."

A string of public meetings has taken place, and there is clearly tension in the air.

The Ruamahanga Whaitua (made up of citizens, iwi and councils' representatives) is recommending that further investigation be undertaken into the hydraulics of the lake — for example, putting the Ruamahanga River back into Lake Wairarapa.

A further option would be to open up another exit channel from Lake Onoke into the sea, perhaps controllable.

"There are alternatives that would enable Lake Wairarapa to hold water for longer to accommodate higher levels," says Smaill. "This could be advantageous."

The arguments also cover the cost of any mitigation scheme — who will pay for it, who can engineer it, and how can flooding be controlled during the process.

It has to be said the Ruamahanga River is not in the greatest of health either. According to the regional council, it is looking good until it starts its run passed Masterton and Carterton, taking in urban and rural run-off and pollution. By the time it flows under the road bridge at the picturesque Gladstone country pub, its levels for nitrogen and phosphorus (although trending down) are in the worst 50per cent of like sites nationally.

Ra Smith, environmental manager for Kahungunu ki Wairarapa, believes the mauri of the Ruamahanga can be restored, and as a member of the Whaitua he is well aware of the issues. He is advocating a win-win approach.

"Te mana o te wai is about the best living for Wairarapa people: the best environmental living, the best economic living, the best social living and the best cultural living. Then the mana of Wairarapa, where water glistens [in Maori] will be fulfilled."

There is still a long way to go in the public consultation process, but the Whaitua would like to see the Ruamahanga flow again into Lake Wairarapa, with floodwaters diverted down the existing man-made channelling. It also proposes a 10-year status quo so more research can be conducted and users can plan any adjustmentseeded.