A new report reveals that the speed of Auckland's population growth poses the biggest threat to the city's environment.
Auckland Council has released its first State of the Environment report since 2009, highlighting the current and potential issues that the city faces.
Auckland's population is expected to hit 2.01 million by 2033. According to the 2013 census, the current population is 1.4 million - 33.4 percent of New Zealand's population.
The 200-page report shows a slow decline in the quality of marine and freshwater since 2010 due to sediment and contaminants, as urban Auckland's footprint expands.
Aucklanders face a moderate to high risk of getting sick from swimming in more than a quarter (28 percent) of the city's swimming spots.
Many of the city's streams were considered of a very poor standard, and the report said of the monitored marine sites, 31 percent had poor water quality, and just 8 percent were deemed "excellent".
All the city's harbours and estuaries were found to have had at least one site with moderate or poor ecological health.
Climate change is also expected to affect Auckland, with increased temperatures, lower average rainfall, more storms and flood events, and sea level rise.
There have been some environmental improvements, however, relating to air quality, pest management and awareness of heritage sites.
Senior scientist at the council's research and evaluation unit, Megan Carbines, co-authored the report. She is hopeful the environmental threat from Auckland's ballooning population can be overcome - as long as change happens now.
She said the decline in water quality was a reflection of Auckland's development, particularly housing, over the past 100 years.
Dr Carbines said it was lucky the city hadn't destroyed its environment beyond repair.
"We've got lots of briliant natural assets that are left, and in a really good condition, so I think we are at a point where we can build on that and make improvements, rather than going drastically backwards."
Air quality better
However, the council's chief operating officer, Dean Kimpton, said air quality had improved in the region, and the shift to electric trains and the City Rail Link would help it to continue to improve.
He said Auckland's expected population increase would certainly put some real pressure on the environment.
"And streams and our beaches are examples of that. But the work that we're doing and want to continue doing in (the) Auckland growing greener initiative are key planks in that."
Mr Kimpton said examples of moves to be more energy efficient included plans for LED lighting across the city, along with composting and recycling initiatives.