KEY POINTS:
The water quality of Auckland's rivers and streams is improving, although it is still the worst in the country and has some "ugly hotspots", says the Auckland Regional Council.
The council has issued a river water quality report based on data collected over 10 years from 25 sites.
The council's monitoring and research group manager, Grant Barnes, said there were some encouraging trends in the majority of the region's rivers.
Nutrients, suspended sediments and faecal bacteria indicators had decreased, which was a positive sign as they were major contributors to poor water quality, he said.
Mr Barnes said it was not clear what had caused the improvements, but it could be partly explained by the installation of storm water ponds which allowed sediment to settle before water was discharged.
He said the downward trend in suspended sediments was particularly welcome as sediment affected not only the rivers but caused problems in harbours.
But although sediment levels were reducing in streams, the Auckland region still had the highest levels in the country.
Many of the region's streams had high concentrations of nutrients and suspended sediments, and high levels of faecal coliform bacteria.
"There is still room for improvement when we compare our streams with the national standards."
The average visibility in Auckland streams was 0.6m, followed by Waikato with 1.1m. Nelson had the best water visibility of 4.7m.
Mr Barnes said the report had highlighted some ugly hotspots which consistently exceeded health guidelines.
Site by site investigations would be needed to ascertain the cause of the problems, he said.
Mr Barnes said the waterways were not used for recreation but "don't look the best".
They had been rated using several indicators including conductivity, faecal coliforms, nitrate, acidity, suspended sediment, temperature and turbidity.
Mr Barnes said the five sites which scored the worst in terms of water quality were all in the Tamaki catchment, reflecting the urban and industrial land use in the area.
The Omaru Creek in Glen Innes had the worst water quality in the survey, just ahead of creeks in Pakuranga and Otaki.
Mr Barnes said the sites which showed up as the clearest and cleanest were in bush-clad areas such as the Cascade stream in the Waitakere Regional Park.
He said waterways in rural areas were showing improvements as residential developments expanded. These reduiced the effect of nutrients, sediment and faecal bacteria from intensive agriculture.
Mr Barnes said the regional trends also showed a warming of water temperatures which could be some indication of a warming climate.
