Many people were unhappy that a playground less than 5m from a waterway, and bordering a car park and park area open to unleashed dogs, was not going to be fenced, parent Lisa Miller said.
"Other playgrounds might have one risk, this has three or four serious issues - it's extreme.
"I don't want it to be one of those situations where we have to wait until someone gets hurt before something is done."
It was possible to keep a close eye on one child, but with two or more children it became difficult.
"I've got a 3-year-old and an 18-month-old who'd love to play there . . . but it's not safe."
She felt so strongly about it she had set up a Facebook group on the internet inviting people to join in her campaign.
"I didn't know what to do. The council needs to listen to us.
"It's not on. These things really matter."
Claress Gladding said she applauded the council for building the playground but could not understand why it could not find the money to fence around it, given other projects on which it was spending money.
Another mother who emailed the Otago Daily Times said it seemed "crazy" that it was illegal to have an unfenced pool, yet the council could build a playground aimed at young children next to a busy car park and an inlet.
Council parks and reserves manager Martin Thompson said the playground would not be fenced, as it was not the council's normal practice to do so.
The design had been consulted on and fencing it did not arise as a strong issue during that process.
"A lot of playgrounds have potential hazards like roads," he said.
The playground was landscaped, with grass mounds between it and a path next to the water, and seating would be placed along the top of the mounds, facing towards the playground, he said.
He urged parents to wait until the playground was finished before developing their final impressions.
Later this year, the council's play strategy would be under review and comments about issues such as fencing playgrounds would be included in wider public consultation, Mr Thompson said.
There was a post-and-paling fence along the car park boundary, and signs would be put up advising that dogs were not allowed in the playground.
WaterSafe Auckland Inc business manager Teresa Stanley said the council had no obligation to fence off a playground from a natural waterway, but "parents have a right to be concerned".
