Ms Brown has long opposed the proposal to raise the wall of the dam in what the government deems to be an effort to protect communities downstream in the Hawkesbury-Nepean Valley from flooding, as many significant Indigenous cultural sites would be inundated and lost forever.
"The whole document is full of mistakes," Ms Brown told the Advertiser.
"Warragamba is referred to as Wallacia more than once.
"One type of flood modelling is used downstream and a different type is used upstream.
"The impact area behind the wall is only based on a 7.2-metre rise in water above the current wall, and not the full level of the new wall. This will mean many sites will be damaged or destroyed and won't be recorded."
Ms Brown questioned the use of predictive modelling based around an investigation of 27 per cent of the area which would be impacted, saying they had no way of knowing exactly what they would be compromising if the entire area was not assessed.
"They say their predictive model is accurate, however that only gives them the numbers of possible sites, it does not tell them what those sites are," she said.
"I don't think the findings are appropriate. Sites that will flood haven't been included because they are outside of the 'impact zone'.
"Non-Indigenous people should not be deciding what is and isn't important to us - the sites are individually rated, the whole area is a site related to the creation story."
Ms Brown also criticised the length and accessibility of the report. Interested residents have until only November 12 to submit their feedback on the project, despite there being thousands of pages to read through.
"I don't think the report is available to everyone," she said.
"It's a huge document many people and many people will struggle to read it online. Many elders don't have internet or only have a phone to read it on.
"You need to create an account online to make a submission, and again, many elders will struggle."
Ms Brown said it was important for everyone to understand that the project is not about increasing Sydney's water supply (not a single extra drop will be saved), and that she and fellow Indigenous locals were not against flood mitigation but believed there were "better options than raising the wall".
Wollondilly Council publicly condemned the EIS in a special meeting last week.