The Hauraki Gulf faces increasing environmental threats from urbanisation of its shores and the growth of dairy farming, says a report by its guardian agencies.
It says the health of the gulf's waters are directly affected by what is flushed from the catchment where one million people now live and dairy cattle are densely stocked.
An updated version of the Hauraki Gulf State of the Environment published three years ago, the report is the work of the Hauraki Gulf Forum, which includes the Auckland Regional Council and Environment Waikato.
It says other threats to one of the country's most popular stretches of water include mud and silt pouring into harbours, pollution, the introduction of exotic pests and erosion.
WATER QUALITY
Aucklanders use more water than they did three years ago - 303 litres a day per person compared with 296.
In January 2007, it was estimated that about 2.9 million cu m of sewage went into the gulf as a result of network overflows in wet weather.