KEY POINTS:
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.
Auckland City has 300km of sewers that also carry stormwater and overflow into local waterways.
However, levels of bad bugs in the water at bathing beaches are not getting worse - thanks to councils making gradual progress in treatment of sewage and stormwater.
About 410,000 dairy cows are now farmed on the Hauraki Plains and stocking densities grew in three years from 2.9 cows per hectare to 3.03.
This combined herd produces the same amount of faecal matter as six million people.
Environment Waikato research shows that Waikato rivers contribute 96 per cent of the total nitrogen entering the gulf.
The western side of the Firth of Thames is most at risk of algal blooms should land discharges of nitrogen increase.
SEDIMENT
Heavy metal contamination in the sediment of Auckland's poorly flushing harbours and estuaries is a continuing threat to marine ecology and solutions need to address the sources, mainly runoff from roads and building materials.
In the Firth, zinc and cadmium runoff from farms will need watching, while nitrogen from paddocks is a potential cause of algal blooms.
In North Shore creeks, zinc concentration increases are attributed to recent large scale urban development.
Sediment from earthworks continues to fill estuaries, allowing mangroves to colonise sand and shell banks.
Such action has displaced some coastal wading bird communities.
The Firth is the only gulf coastal area being monitored by Environment Waikato for sediment changes.
Chemical contamination of Auckland shellfish is low by international standards and shows no deterioration.
DEVELOPMENT
The picture-postcard image of the gulf is changing. On the Coromandel Peninsula, the number of homes grew by 18 per cent or 2664 between 2001 and 2006.
Visitors numbers edged towards two million a year.
The coastline from the Auckland Isthmus to the Mahurangi Harbour is highly urbanised, with regional parks providing buffers to settlements.
More than 60 per cent of the gulf coastline is now adjacent to publicly-owned land.
The land to the north of Pakiri remains the only large area of private undeveloped beachfront along the northern coast. However, a development is planned for Te Arai Pt.
Ten camping grounds have been lost on the Coromandel Peninsula since 2000. Recently, consent was granted to develop the Cooks Beach camping ground for residential purposes and one new camping ground has been added.
