NSW firefighters have saved the last of the so-called “dinosaur trees” remaining in the wild after dousing the Wollemi National Park with fire retardant and laying an irrigation system during the recent bushfire crisis.

On Wednesday the government confirmed efforts by the NSW National Parks and Wildlife Service and NSW Rural Fire Service had ensured that the wild Wollemi pines survived the Gospers Mountain megablaze.

The trees in the national park have grown since the age of the dinosaurs.

The operation involved using large air tankers to douse the remote area with fire retardant and specialists firefighters being dropped into the site from helicopters to lay an irrigation system.

NSW Environment Minister Matt Kean says while some trees were damaged, the species would survive the fires.

“The 2019 wildfire is the first-ever opportunity to see the fire response of mature Wollemi pines in a natural setting, which will help us refine the way we manage fire in these sites long-term,” he said in a statement.

“Illegal visitation remains a significant threat to the Wollemi pine’s survival in the wild due to the risk of trampling regenerating plants and introducing diseases which could devastate the remaining populations and their recovery.”

Meanwhile, bushfire-ravaged communities are preparing ahead of forecast heavy rainfalls that authorities fear could impact water quality and cause landslips and flooding.

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Rainfall totals of 30 to 80 millimetres are forecast from Thursday, with strong falls possible for fire grounds in the Snowy Mountains, southwest of Sydney and south coast regions.

Water NSW said it is preparing to limit potential impacts on the water quality in dam storages caused by ash run off but the rain forecast this week is not considered intense enough to wash material into catchments.

Chief executive David Harris said no water quality problem is expected this week but catchments will need to be managed to protect water supplies in the coming months.

Several precautionary measures have been taken including using silt curtains to stop ash being washed into Warragamba Dam by heavy rainfall.

Firefighters have welcomed the forecast as the best news in months but the Bureau of Meteorology says there’s a downside.

“Hopefully some of this heavy rainfall will fall over fire sites and help control or even extinguish fires,” meteorologist Sarah Scully has said.

“But it’s a bit of a double-edged sword because heavy rainfall and gusty thunderstorms bring the potential for flash flooding, particularly in the burnt-out areas of NSW and Victoria which are now vulnerable to landslips and trees coming down.”

Despite the easing conditions, fire danger ratings were still high for large parts of NSW on Wednesday.