It will be months before Mataura residents know the full extent of the flooding risk after discovering capacity issues with their stop banks.

Last week, Environment Southland announced residents in Gore, Mataura and Wyndham may need to evacuate sooner than originally planned, and it was undertaking more investigations.

On Friday, the regional council held its first drop-in information session in Mataura to hear residents concerns and provide answers.

It was a calm, sunny day in Mataura, but residents said flooding was not far from their minds.

Sharon Argyle has lived in Mataura all her life, remembering evacuating at 2am with her parents in the 1978 floods.

Mataura resident Sharon Argyle. Photo: RNZ / Tess Brunton

"We lost our car, but we didn't lose anything inside the house. My cat was dry," Argyle said.

"But there was a lot of people worse off than us. They lost everything. The water went through their home and out the window. It was terrible."

Flood protection had improved since then but more work was needed, she said.

Leaving Environment Southland's information session, she said she wanted a lot more answers and a public meeting.

"[They] don't seem to know what they're going to do. I think ... they should have a look at the river bank a lot more, see what they can do about that, those stones. To me, I've just gone in and I've come back out and I haven't got any satisfaction."

Mataura River. Photo: RNZ / Tess Brunton

Mataura resident Tali McLean said much of her property was underwater during the February 2020 flood.

She was worried about the next flood and what would happen if the stop banks were not strengthened in time.

"There's always that thought in the back of my mind 'do I stay, do I go, do I stay?' Who knows."

Mataura resident Gaylene Adams, who has lived in Mataura for the past 40 years, said the 2020 February floods were the worst with widespread evacuations.

Mataura resident Gaylene Adams says it took a long time for the town to get back to normality after the 2020 February floods. Photo: RNZ / Tess Brunton

"I was sort of stuck because I live on my own and I was evacuated at six o'clock in the morning.

"It took a lot to get the town back into normality for people."

There were a lot of older people who were in similar positions, and either had to rely on family, Civil Defence or Fire and Emergency to help them evacuate, she said.

Environment Southland maintains more than 100 kilometres of stop banks on the Mataura River.

Integrated catchment management general manager Paul Hulse said it was expected to take six months of further investigations before the full extent of the issues - including construction concerns - were known.

Environment Southland integrated catchment management general manager Paul Hulse. Photo: RNZ / Tess Brunton

"What we now need to do is look forward with the fact that climate change is a issue, with the fact that we're going to experience higher flood levels, longer peaks, and come back with a solution that addresses those changes for the next 30 years."

They would still have nine to 12 hours heads up before a big flood, he said.

Emergency Management Southland manager Simon Mapp did not want the community to be scared, he wanted them to be prepared.

"We would advice the mayors very early that declaration might be the idea so we'd be doing that at a lower level.

"Now I can't give you an exact cumec level, but we would be a lot more conservative to actually evacuate people to ensure their safety."

There will be more information sessions in Mataura, Gore and Wyndham in the coming weeks.