Surf lifesavers are refusing to patrol and ocean swim events have been regularly cancelled as Auckland beaches suffer from a growing pollution problem.
Eighteen no-swim notices are currently posted around the Auckland - 14 indefinitely.
One of the beaches affected is Takapuna, previously a jewel in the region's crown, which carried a 'high risk' water quality rating earlier this week.
Takapuna Beach Series organiser Nick Carroll told RNZ he had previously only cancelled two swim events over 12 years. In the past four months, he's pulled the pin six times due to water quality.
"It's basically ruined the image of the Beach Series," he said. "People only have so much time to spend doing recreation, they may not bother with the Beach Series where it's 50-50 each week whether it's on.
"I'd say the writing is on the wall for ocean swimming. A lot of people may move away from ocean swimming as a result of what Auckland Council has done here - or hasn't done."
Mr Carroll plans to move his series away from its traditional home to a safe beach next summer.
A triathlon at Clark's Beach on the Manukau Harbour has had to drop its swim leg and convert to a duathlon (run/bike/run), after lifeguards refused to oversee the race in high-risk conditions.
Surf Life Saving services manager Allan Munday told RNZ it would be "irresponsible" to put lifeguards at risk at an event where competitors chose to put themselves in harm's way.
He also admitted lifeguards were finding it difficult to train regularly in the current conditions.
In a statement to RNZ, Auckland Council acknowledged it had underinvested in water infrastructure, but planned to address that in the latest rate proposals.