Politicians and the public are being urged to take swift action to reverse the fortunes of one of the country's most significant and treasured marine parks.
The State of the Hauraki Gulf 2017 report says unprecedented pollution and population growth is causing huge harm to wildlife and beaches.
The Hauraki Gulf is considered a marine paradise for hundreds of thousands of beach-goers and boaties. But it's a resource increasingly under pressure.
"What I'm asking is that we need to start making some changes today because if we leave it for another 20 years or 25 years, the cost will be horrendous", Hauraki Gulf forum chairman John Tregidga told Newshub.
The report paints a bleak picture. Among a range of facts and figures, it states that 34 percent of kiwis live in Auckland and that the population is expected to exceed 2 million in 15 years.
According to the report's estimates, the Gulf supports 45 percent less fish than it did in 1925.
Since 2014, 66 new marina berths and 12 jetties or boat ramps have been created.
In Auckland, half of all monitored beaches have exceeded contamination levels at least once and 882,000 metric tonnes of rubbish was removed from the coast between 2014 and 2016 by the Watercare Harbour Clean-Up Trust.
"We've lost major habitats like mussel beds from the Hauraki Gulf. We've got thick layers of mud through large parts of the Gulf now, such as the Firth of Thames," says environmental consultant Dr Shane Kelly.
Other alarming data relates to snapper numbers, which are down by 83 percent on historic levels. Crayfish, which keep reef ecosystems healthy, are in an even poorer state.
"They're at a point now where they're probably at the lowest levels ever seen in the Hauraki Gulf," says Dr Kelly.
There have been plenty of warning signs about poor water quality and contamination on beaches around Auckland this summer. Sixteen different bays and beaches around the city are currently classified as 'no swimming' zones.
Part of the problem according to Dr Kelly is that much of Auckland's stormwater infrastructure was installed 75 years ago and it just can't cope.
Sam Judd from rubbish clean-up and waste education charity Sustainable Coastlines says we should be in a position where we can swim at all of Auckland's beaches at any time of the year.
"Our kids are getting sick from going to the beach and that is quite frankly wrong," Mr Judd says.
He says thoughtless consumption and littering contributes to a related problem, especially when it comes to wildlife.
He showed Newshub a collection of plastic wrappers and fishing gear, which Mr Judd says was removed from the guts of local turtles. He says there's evidence our favourite table fish, the Snapper, are also consuming plastic.
"We need to think about the plastics that we are consuming and stop buying single-use plastics, and the rest is just 'don't drop it on the street'," says Mr Judd.
Mr Judd points to planting trees near waterways as another simple method of filtering out nutrient and sediment runoff.
To turn the tide, the report authors want action on the 2016 initiative called Sea Change.
That plan includes banning some commercial fishing methods, creating marine sanctuaries and setting limits for sediment and nutrient run off.
Forest and Bird's Hauraki Gulf advocate Alicia Bullock is urging the Government to adopt the Sea Change recommendations.
"Bottom trawling is incredibly destructive," she said. "It wipes out the seabed leaving effectively a desert behind. So that's one of the really important recommendations that needs to be implemented."
"We are not seeing real commitment from central and local government in making changes", says Mr Tregidga.
The Conservation Minister lays blame with what she calls the previous Government's inaction. Eugenie Sage says she won't leave the report sitting on the shelf, but warns changes "won't happen overnight".