Water Safety general manager of partnerships Gavin Walker told RNZ no amount of social media views was worth people risking their lives.
"Jumping off places like bridges, there is a fairly high risk of something going wrong," he said.
Mr Walker wanted people to realise the danger.
"The more challenging thing that we’d love people to think about is even the strongest swimmers can encounter issues with currents and tides in locations like under the harbour bridge," he said.
"It’s one thing to do the jump, it’s another thing to get back safe ... "
Hitting the water the wrong way could quite easily knock someone out, Mr Walker said.
There was also the risk of boats.
"There’s always the risk of boats coming through that are obscured from your view, so you don’t actually know that they’re coming through, and they can’t tell that somebody’s about to jump," he said.
If people wanted to jump into water, they should do it where it was safe, Mr Walker said.
"Bridges are notorious for having kind of hidden hazards underneath them, so things like logs and other things trapped around them and the current swirling around tend to move logs and sand banks around quite easily."
The Auckland harbour itself was a challenging place to swim, he said.
"Depending on the tidal conditions and currents on the day and time, it can be quite difficult, more difficult than people think, to get back to shore."
He did not want people to underestimate the challenge.
"Look, it’s beautiful weather and these things always look like great fun, but there are other places where you can go and have fun and do that more safely."
He wanted swimmers to make good choices when getting into the water.
"These are the days where we love getting into the water, but we need to look after each other so that we don’t have tragedy."
Another video posted last year on a separate account also showed two people hanging from underneath the bridge before dropping into the water.
New Zealand Transport Agency Waka Kotahi (NZTA) told RNZ the bridge jump in the video was illegal and dangerous.
"Pedestrian access to the bridge is strictly prohibited as it is part of the motorway network and is a hazardous area, and the potential for serious injury from such illegal access is high."
A spokesperson said NZTA was investigating the incident and would pass any relevant information to police.
Access was controlled by security fencing and electronic gates, and NZTA would review security as part of the investigation, they said.
Police said they were not immediately aware of any reports.
