Mrs Webster said the council put a lot of money into the park and the society had done great work.
The park is 80 minutes' drive north of Auckland between Warkworth and Leigh and the last 6km of the access road has a gravel surface.
Mrs Webster said that bit put off a lot of potential visitors because it was a "deadly mixture" of narrow parts and blind corners.
"If we are going to have regional parks we should allow people to get there in an easy way. We want people to go there ... we can't have all this money tied up in parks and not encourage them. But we don't want them killed either."
Her comments outraged Councillors Sandra Coney and Mike Lee, who expanded the parks network during their terms on the old regional council.
"I'm astounded," said Ms Coney, who now chairs the Super City's parks, recreation and heritage forum.
Mr Lee, a former ARC chairman, responded: "It's an absolute lie and a very unfair statement on these dedicated staff and volunteers."
Society chairman Steve Palmer said he could not speak for all members but he was not in favour of extending the tarseal because it would encourage visitors to speed.
"Someone would have to assure me that the road is widened as well to avoid head-on collisions on those blind corners. I think it is safer left as it is but with work concentrated on improving corners.
"The road is not keeping people out but some individuals among us would say that having a few kilometres of unsealed road enhances the feeling of isolation, of being away from the city, which most of our visitors are seeking."
Bruce Wells, who owns the luxury Sandpiper Lodge near the park, said the road was dangerous but did not seem to deter visitors.
"It's like the old roads you used to drive when you went off surfing."
