A group of Hawkesbury residents has slammed NSW's water authority and the Bureau of Meteorology over the handling of this week's flood "catastrophe" and failure to reduce Warragamba Dam levels.
The residents, who have formed a group called Richmond Matters, say they had been warning authorities for several years more needed to be done to prevent a major local flood.
The group said the scale of flooding in northwest Sydney, which has cut off communities and inundated properties, could have been avoided.
"I'd written to the government with my concerns about this, that there really needed to be some well thought out program starting mid-last year to release water from the dam," member Samantha Magnusson told AAP.
"There was no response, I didn't get a response.
"We wanted there to be a staged release of significant amounts of water so that we weren't sitting in the position that we're in now."
Ms Magnusson and her husband breed showjumping horses near Richmond and were required to evacuate their horses.
She said disbelief had turned to anger for many along the Hawkesbury, with the risks of residing on the flood plain well understood.
"We have been very concerned for about a year ... we knew that with the predicted La Nina weather that this would be significantly worse because the dam was sitting at almost 100 per cent capacity."
NSW Water Minister Melinda Pavey this week defended decisions around the release of dam water and said there was no way of avoiding the spill.
Water NSW said the dam would need to be drawn down to an unprecedented 25 per cent to avoid flooding from the spill-over.
This week's "rain bomb" meant the dam was 75 per cent over capacity, sending about three Sydney Harbours worth of water flowing down the valley.
Ms Magnusson also criticised the BOM over the speed of the evacuation warnings for Richmond.
"All of a sudden the river rose metres in hours and we were literally running around to get out ... we were going from minor flood warnings to potentially catastrophic in less than 12 hours," Ms Magnusson said.
The Bureau of Meteorology told AAP residents were warned on March 17 heavy rainfall may hit Sydney.
"By Thursday 18 March there was a significant increase in the amount of rainfall forecast for the Hawkesbury-Nepean catchment for the following weekend," a spokesperson said in a statement.
"The Bureau began warning residents of the potential for a 'life threatening' weather event."
While Ms Magnusson got her own horses out, she spent days with neighbour Hugh Parry-Okeden helping rescue other people's animals.
Mr Parry-Okeden's 12-hectare property was cut off by floodwaters for six days. His wife Gendy and their three children haven't been able to return.
"We found 18 stranded cattle in trees and they were quite distressed," the former Australian polo player told AAP.
Ms Parry-Okeden is now seeking a water storage and flood mitigation inquiry.
"Why didn't we let water out of the Warragamba some months ago, we could have at least taken the edge off the severity of what we've seen," she told AAP.
"There were plenty of my neighbours who were left flat-footed purely because the warnings weren't good enough ... within six hours we were all re-moving livestock and houses were already too hard to get back to."
Local activist groups such as The Colong Foundation also argue volume of water in Warragamba Dam should be reduced even if it only plays a minor role in flood mitigation.
However they are opposed to proposals to raise the dam wall.