Flooding in the area on the western side of Lake Onoke this month. PHOTO/SUPPLIED

ELISA VORSTER

elisa.vorster@age.co.nz

Negative impacts on endangered birds, spawning fish, and wetlands from rising lake levels on Lake Onoke could have been avoided had the lake mouth been opened sooner, says conservationist Dougal MacKenzie.

The mouth was reopened by the Greater Wellington Regional Council (GWRC) last week as part of a scheme implemented in the 1970s to prevent mass flood damage to surrounding farmlands.

Lake Ferry resident, Mary Tipoki, opposed the opening after expressing both environmental and cultural concerns, the sources of dissent for more than 150 years.

She saw no reason for the lake’s water to be manually drained.

But Mr MacKenzie said the high lake levels in the last three months, and delay in opening the mouth, had seen the area left with rotting and dying plants.

“If you saw it at the moment and since it was opened, there’s black, dead grass – a stinking mess if you like.”

He said the mouth opening was a “complex issue”, with conservation being equally as important as farming, cultural and environmental interests.

When European farmers settled in the area, there was no other option but to open the lake mouth manually, he said, but this ruled out any conservation concerns as it destroyed up to 95 per cent of pristine wetland.

Better efforts were needed to prevent the negative environmental effects of letting the lake level get as high as it did this month, he said.

“We can’t turn the clock back.

“What we can do is have better control over the level of the lake.”

Mr MacKenzie said a major conservation issue was the impact on rare and endangered birds in the area, such as the Australasian Bittern, which relied on the wetlands on the western side of the lake for nesting.

With the high lake levels overflowing into the wetlands, these birds had “no chance whatsoever” of nesting.

“In fact, it probably knocked quite a few of those birds that were on nests out of action.”

According to the Department of Conservation website, there are less than 1000 Australasian bittern in New Zealand and the bird is globally endangered.

The delay in opening the mouth also prevented mullet from re-entering the wetland area to lay their eggs.

As a resident in the area since 1984, Mr MacKenzie said he understood both cultural and farming views.

He was aware Maori wanted the area to be flooded because it was a breeding ground for eel “and that still is pretty important”.

He also acknowledged it was vital to prevent a repeat of the large flood in 1947 that affected many farming properties.

“You’ve got farming interests, you’ve got the interests that Mary Tipoki is talking about and then you’ve got environmental interests or conservation interests.”

A spokesperson from GWRC said the lake closed naturally due to low flows from the upper catchment mixed with southerly swells and could close anywhere between five and 15 times per year.

The council’s aim is to keep the lake open at all times as part of their flood management scheme but the reopening of the mouth was dependent on the right environmental conditions.