Safeswim technical leader Dr Martin Neale said some of the warnings were due to heavy rain washing contamination from land into the ocean.
He said several of these warnings were related to a less common occurrence, triggered by wastewater overflows.
"If we get intense rain events, the stormwater can get into the wastewater system and cause the pipes to overflow," he said.
Neale pointed out Safeswim water quality alerts had only launched late last year.
While we were seeing warnings issued more frequently, this was largely due to greater availability of information.
However, Neale said the widespread heavy rain that had soaked the Auckland region over the weekend had caused beach warnings to be issued on a scale he hadn't seen so far this summer.
The spread of water quality warnings stretched up to Orewa. The beach, on Auckland's Hibiscus Coast, had been hit hard by stormy weather this summer.
A 16-year-old lifeguard from Orewa Surf Lifesaving Club said the beach patrol had been stood down this weekend due to brown, dirty water and "no swimming" notices.
"We have been unable to open the beach for swimming, as well as trainings being cancelled or being moved to Hatfield's beach, which is apparently safer."
The lifeguard, who did not want to be named, said it was disappointing for lifeguards who were not able to train for their competitions.
Speaking to the Herald yesterday afternoon, Auckland mayor Phil Goff said there was a scheme in his 10-Year Plan to separate stormwater from wastewater.
This, along with a major new central wastewater interceptor in the pipeline, would help prevent future wastewater overflows.
Goff said more intensive housing and major weather events were putting pressure on the city's wastewater system.
"It's time, if we want to be a world-class city in the 21st century, actually to take real action to bring it to an end.
"A higher population, more frequent heavy rainfall events, will exacerbate this problem and make it worse."
