The NSW Government has been warned about its latest dam-raising plan. 

During the state’s most recent drought, the NSW government announced plans to raise the Wyangala Dam level by 10 metres.

The project is intended to add another 650 gigalitres to the total storage capacity, an increase of over 50 per cent.

Water NSW estimates the enhanced storage will provide an extra 21 gigalitres per year for general security water users on average.

The NSW and federal governments have committed $650 million to the project, but a parliamentary inquiry has found that the cost of the project will be as high as $2 billion.

NSW Water Minister Melinda Pavey says the state government remains fully committed to the Wyangala project, despite its increased costs and delays.

Farmers have accused the NSW government of trying to flood one agricultural region to provide water further downstream, “robbing Peter to pay Paul”. 

Upper Lachlan Branch of the NSW Farmers' Association chair Robyn Alders says simply building a bigger dam is “a 19th-century solution to a 21st-century problem”. 

She also said there was no consultation with farmers upstream of the dam, nor proper consideration of other ways to improve water security.

UNSW water infrastructure expert Professor Stuart Khan points out that the state cannot generate more water. 

“The thing we need to remember about the Murray-Darling Basin is that it's a fully allocated system - there's no spare water,” he said.

“If we want to make more water available for one person, we'll be taking that water from some other use, be that an environmental use or be that an allocation somewhere.”

Professor Khan said increasing the size of the dam may only reduce flows to the wetlands at the bottom of the river, which fill groundwater reserves.

“So those groundwater systems will be missing out on water, and you have big swamps and you have big wetlands that are very environmentally significant wetlands,” he said.