Brighter future for murky waters

Rotoehu means muddy or murky lake - but Maori who named the area could not have foreseen how inhospitable the water would become.

Blue-green algal blooms have plagued Lake Rotoehu every summer since 1994, making it unsafe for people to have skin contact with the water. As a result, it is one of the region's sickest lakes.

Tucked between Lake Rotoiti and Lake Rotoma, Lake Rotoehu has 50 or so houses dotted around its edge. Motorists catch only a brief glimpse of it as they travel along State Highway 30 which links Rotorua and Whakatane.

But away from the public gaze, Environment Bay of Plenty, the Rotorua District Council and Maori landowners have been working hard to improve Lake Rotoehu's water quality.

Before 1996, cattle and sheep roamed across paddocks which led right down to the water. Two large farms owned by Tautara Matawhaura Lands Trust cover almost half of the lake's catchment area and were responsible for large amounts of nitrogen and phosphorus entering the water through fertiliser, soil erosion and animal effluent.

But after several years of negotiations with the trust, planting and fencing work began on the Matawhaura farm, in the lake's northwestern corner, to curb nutrient input in the hope the lake's health would eventually recover.

Seven years on, the transformation is impressive.

Hills on the farm which rise from the water's edge are now neatly fenced and blanketed by cabbage trees, flax, manuka and other native species. Stock numbers have been reduced and tall eucalyptus trees have been planted as a replacement income source.

"The main aim initially was to get the stock out of the lake," said Environment BOP soil conservator John Douglas, who oversaw the planting project.

"The other thing we wanted to do was enhance the bush areas already established around here."

A boat ride around the shoreline to places where sheep still roam reveals the impact they have had on native bush since the area was cleared for farming in the early 1900s.

"The animals just trample all the roots and chew the bark on a lot of the trees that were in here," Mr Douglas said.

"If you can picture that large parts of the lake have been like this the last 70 years, you can start to fathom why the lake's in the state it is."

On the Matawhaura farm about 45,000 native seedlings have been planted, 11km of the lake's edge has been fenced, and more than 150ha has been retired from grazing.

Environment BOP is turning its attention to the trust's second farm and a small neighbouring dairy block in the hope of similar results.

Much of Lake Rotoehu's nitrogen and phosphorus comes from beneath the water. Due to algal growth, the sediments on the lakebed can no longer successfully store excess nutrients as they have in the past.

That process cannot be controlled, but the regional council hopes cutting the amount of nutrients entering the water from external sources will - in time - help the lake to recover.

Environment BOP soil conservator Colin Stace said the restoration of wetlands would be crucial in achieving that reduction.

Reed beds, which existed around the lake's edge before being eaten and trampled by stock, help create conditions where nitrogen in the water can be turned into gas and released into the atmosphere.

A wetland has been established in the lake's northwestern corner and there are plans for more.

But when dealing with Rotorua's lakes, Environment BOP must develop a relationship with the landowner and gain their support before any work can occur, Mr Stace said.

"The programmes are voluntary because it's quite important that the landowners do identify with the issues and take an active role.

"Once the initial work is done such as fencing or planting, on-going maintenance is required and that falls on the landowner - so if they're not willing partners there's a bit of a problem."

Landowners were often cautious because part of the deal involved signing a covenant which protects the environmental work by ensuring it could not be undone in future.

"People are often worried that it creates a right of public access to their land. It doesn't, but we need to explain that."

After increased publicity this year about the health of the region's lakes, more and more landowners wanted to take advantage of subsidies offered by local authorities and get environmental protection work done, Mr Stace said.

In the case of Lake Rotoehu, the Tautara Matawhaura Lands Trust said it was happy to work with Environment BOP.

The trust's 1400 beneficiaries were keen to diversify their business interests and areas of land around the lake were better suited to forestry than farming.

Trust chairman Joe Malcolm said: "We had a responsibility to do something. At the end of the day it looks wonderful and who knows what it will be like in 10 or 20 years."