Group tells NSW premier 'don't raise dam'

A group of scientists has written to the NSW premier over her government's plan to raise the Warragamba Dam wall which they claim will endanger two national parks and breach World Heritage List conventions.

The government in September introduced draft legislation to parliament to extend the height of the Warragamba Dam wall by 14 metres which it says will prevent flooding during a major weather event.

But, if the higher dam reaches 100 per cent capacity, water levels upstream would see new areas of bushland inundated for up to two weeks.

The group of 20 scientists, park managers and former environment ministers - including Peter Garrett - accused the government of pandering to developers who are eyeing downstream flood plains.

"It is evident that housing development of downstream flood plains is a key driving factor for the dam wall raising proposal," the letter released on Tuesday states.

The group says the impact of temporarily flooding the heritage-listed Blue Mountains and Nattai national parks - where at least 25 threatened species live - would be irreversible.