A large bush fire near Bluff this month pressed the reset button on wetland conservation efforts that were almost 15 years in the making.

The Department of Conservation (DOC) will have to dedicate additional resources to prevent aggressive weeds from gaining ground for a second time at the Seaward Moss Conservation Area near Bluff.

The flames of the approximately 30ha bush fire along the northern side of Awarua Bay were easily visible from Invercargill the night of duck shooting opening weekend this month.

While no-one was injured and no properties damaged (except for potentially a couple of maimais), DOC senior biodiversity ranger Jolie Hazley said the burnt earth translated to fertile ground for 

more aggressive pest plants like gorse and a "garden escapee" called Spanish heath. 

"[The fire] opens up all this spare ground that's lovely and fertile to anything that wanted to grow there," she said.

This month's bush fire at the Seaward Moss Conservation Area left the 30 hectares of scorched earth. It will take years before native wildlife returns to nest. PHOTO: Sarah Crump/DOC

Mrs Hazley said efforts to rid the special wetland area of these weeds were almost 15 years in the making after a much larger, 1300ha bush fire ravaged the same area in 2005.

The 2005 fire essentially put those pest species and the area's native manuka neighbours back at the starting line, with the Spanish heath and gorse having the advantage of being able to take off much faster than the manuka.

"There would have been [in 2005] some existing Spanish heath seeds there that we know of, but what we think — no guarantees here — that a lot of other Spanish heath seeds actually blew over from Omaui to the Seaward Moss reserve."

The wetland and its greater surroundings comprise an internationally recognised wetland site, with numerous conservation projects not only happening on DOC land but across the whole Waituna catchment.

Mrs Hazley said weed control work following that first fire cost at least $200,000 in equipment and helicopters alone, and months were spent each year out in the affected area to make sure the native bush came back. 

Fourteen years later, she said the area was taken over by natives, and the skeletons of the recently burnt manuka trees gave insight into how well used the area was for nesting.

"It was noted by one of the DOC crew who was firefighting down there they were amazed at the number of bird's nests that are just still sitting in the trees."

While this month's fire was much smaller in comparison, Mrs Hazley said they were still "absolutely gutted" at its effects on animal life like fernbirds and bitterns. 

"They won't be returning to that area until the vegetation starts growing again because it's just barren ground there now.... Any number having to pick up and move next door is unfortunate, and it will be a number of years before they will move back in."

Mrs Hazley expected DOC would have to keep an eye out for weed growth for the next few years, likely a week's worth of work every year.

"It's still time, and it's time that's got to be taken away from another project."