Protection society claims $33.5 million Skypath could affect birdlife and bring extra traffic.
Custodians of bush and recreational areas near Auckland's Northcote Pt fear environmental degradation from a walking and cycling path across the harbour bridge.
Little Shoal Bay Protection Society chairman Jeremy Richards told planning commissioners yesterday the $33.5 million Skypath would bring extra traffic past "a rare and complex ecological area and an outstanding multi-faceted recreational area".
Bird life in the bay and neighbouring Le Roys Bush would be alienated, and the air and water runoff where many children swam would be polluted.
That was queried by Jenny Hudson, one of four commissioners hearing a resource consent application, after evidence from project supporters that most users would prefer to walk or cycle to Skypath.
"We heard evidence there are not likely to be that many vehicles - people are not going to drive to Skypath to get on bikes," she said.
Mr Richards, a Northcote Pt resident, said his group would be "very happy" to see more cyclists and pedestrians in Little Shoal Bay.
But others would want to come by car, and Skypath documentation was silent on the traffic effects beyond the project's northern landing.
Traffic concerns were also raised by The Wharf, operator of a reception centre at Northcote Pt's ferry terminal.
The company says it is required to reimburse Auckland Council's maintenance costs for a bus turning area there, and wants 35 parking spaces reserved for its patrons.
General manager Martin Smith also had concerns about construction noise.
But commissioner Mark Farnsworth suggested he was "making a mountain out of a molehill" and Skypath lawyer Daniel Minhinnick said pile-driving where the pathway would descend from the bridge to Northcote Pt would take only three weeks.
Auckland Tourism, Events and Economic Development (Ateed) chief executive Brett O'Riley, a former Northcote Pt resident designated Skypath's project sponsor for the Auckland Council group, said it would fill a critical missing gap in walking and cycling networks.
Auckland Transport had designated it the region's "number one" walking and cycling project because of that.
Asked by Mr Farnsworth why the council was not therefore developing Skypath itself, he said it was conscious of financial pressure on ratepayers and saw the project as an opportunity for private sector involvement.
The pathway is to be financed by the private PIP infrastructure investment fund, which will be repaid by tolls of about $3 a crossing for up to 25 years.
Cycling Advocates' Network project manager Richard Barter said pedallers around the country were looking forward to a favourable result from the hearing, and Skypath would also give tourists an enduring memory of Auckland.
Referring to concerns of residents, more of whom will be heard today, he said that as the Puketapapa Local Board's previous chairman he pushed cycling paths through "deepest Mt Roskill" where security fears had since eased because of the extra people in parks.
He said roading corridors represented a large amount of publicly owned open space which was dominated by one group of users - motorists - while turning walkers and cyclists into second-class citizens.
"This piece of infrastructure [Skypath] is honouring people who choose active modes."