Boral is currently seeking approval from the NSW Planning Department to "expand" its Dunmore Lakes mine and dig two new sand mining pits (5A and 5B) - the latter would be within 150 metres of the river wetlands.

Both councils have already denounced the plans with concerns over the "potential impact on flora and fauna likely to be significant and has not been evaluated sufficiently".

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Post-extraction, Boral said it would rehabilitate the Stage 5A area, filling it with natural materials and vegetation to return the land to pasture. The 5B pit would "be left as a freshwater pond".

A peaceful protest was held at James Oats Reserve in Minnamurra on Sunday, many in support holding placards opposing the mine.

It culminated in a human message for Boral, spelling out "no boral sand mine" on the hill.

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Community consideration should be given more weight when government bodies decide on major planning proposals, according to environmental advocates for Minnamurra River.

Despite widespread disapproval of a new Boral sand mine in the region - including opposition from both Kiama and Shellharbour Councils - the proposal is still under review.

"We've got a problem with the law when communities have to spend months and months making submissions, rallying to protect the future," Independent MP Justin Field said.

"If you've got two councils and they've got environmental experts ... they've got a really good understanding of the local environmental impacts and I would hope those factual assessments and considerations would be fairly considered."

Mr Field said an "unreasonable degree of weight" was given to the economic value of a project over social and environment impacts in matters such as this.

He also said Boral's plan to amend a current approval for Dunmore Lakes wasn't fair as the new works were "more than a kilometer away" from currently operating sites and in a different catchment

Warren Holder of the Gerroa Environmental Protection Society said he and Mr Field have offered to work with the company to find another, more suitable site.

Mr Holder held grave fears for the current proposal as he said up to 90 Bangalow trees would be removed - home to dozens of endangered and threatened animal species.

"Fourty-one species were recognised to be living in that community, of which 20 Boral [did not recognise]," he said. "They say 20, we say closer to 41."

Mr Field said it was likely Boral's proposal would be referred to an independent planning commission due to the widespread condemnation.

"The fact it's got local opposition is quite significant in terms of how the Planning Department considers the matter," he said.