The new two-lane bridge at Taipā was designed with a platform for leaping into the river, but the NZTA has now erected signs warning that it would be dangerous to use it.
Signs "strongly advising" parents to discourage children from jumping from the bridge are reportedly to be erected.
"While the original plan was to provide a jumping/swimming platform, a recent health and safety review by the project team found that it would not be possible to provide such a platform where it would be safe to jump at all times," NZTA portfolio manager Stephen Collett said.
"The NZ Transport Agency does not condone jumping off the bridge, as it is potentially dangerous, with the possibility of injuries from submerged hazards, rocks, floating debris and passing boats.
"The risk of injury from submerged hazards and rocks is particularly significant at low tide."