Peterborough Residents Group chairman Ronald Irvine said the river mouth had been blocked since November 5 and high rainfall had caused the river to rise rapidly causing flooding issues all along the river.

"We knew that as soon as we got all that rain and the river rose quickly that if it wasn't let out straight away the water would sit there for months," he said.

Mr Irvine said the flooding has caused "total destruction" of the Curdievale recreation area by the bridge near Boggy Creek pub, and had wiped out five years worth of tree planting in the wetland areas.

He said the playground, toilet block and sewerage system had been under water and there were concerns sewerage was ending up in the river.

"The situation at Peterborough is just as bad. The river is right up around the whole of the river mouth and steps where you go down from the children's playground goes straight into water," he said.

"It's created a huge problem," he said.

Mr Irvine said residents had tried to get the river mouth opened by Parks Victoria, who were keen to do it, but they needed to get authority from the Corangamite Hopkins Catchment Management Authority.

"An they're still refusing to open it because it's not at the required level," he said.

"We know the situation on the river. We don't sit in an office in Colac,

"They're worried about a fish kill, but the trouble is they're creating a situation where a fish kill will happen because all the fish are moving out over the wetland areas and when the water eventually goes out, the fish will be trapped on those wetland areas.

"We've never had a fish kill in this river. We just say they're being too precious about the whole thing.

"The trouble is, we've tested the water and it's over 90 per cent fresh water in there which is not good for the fish that are in there anyway. It's an estuarine river."

Mr Irvine said the authority didn't believe that if they opened the river, the water would go out.

"But we have done it in the past and it has gone out and it's then closed up and resumed its normal status," he said.

"If they'd consulted the community about it and opened it in the first place then we wouldn't have had this problem at all."

Residents have called for more consultation from authorities, and want the trigger point of 1.3 metres to be more flexible for exceptional circumstances.

"Every now and then you get an exceptional circumstance like this where you have to take immediate action or you're left with a problem," he said.

Residents were concerned that if nothing was done they could end up with blue-green algae in the river, something that has happened in the past.

Mr Irvine said the caravan park in Peterborough had not flooded like it had in recent years, "but it's not far off it".

"We've had several exceptional events. One was where the river rose very quickly and we had to call emergency services to get the river open," he said.

Mr Irvine said they had been given a "very large" grant to plant trees in the wetlands at Peterborough, which they have done over the past four or five years.

"We spent a lot of work and time planting trees that was suitable for the wetland area and now the water's all over it for three months and they're all dead," he said.

Mr Irvine said one of the problems was there was too many authorities involved.

"When I was a child we used to do it with shovels, and over the years my father and then me have coordinated with whoever the authorities were and we've never had problems like we're having now," he said.

"People sitting in offices that have no correlation with the problem are making the decisions."

The authority has been contacted for comment.

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