Fourteen per cent of monitored beaches in New Zealand are classified as "high risk" for water quality issues - but the rest are either suitable or excellent for swimming.
An extension to the new website, Land, Air, Water Aotearoa (LAWA), which provides water quality information on 350 beaches around the country, was this morning launched at Wellington's Oriental Bay by Environment Minister Dr Nick Smith.
Along with river information, LAWA now gives a seasonal guide to beaches' water quality based on the last three years of monitoring as, well as the results of weekly beach testing.
Read together, the seasonal indicator and weekly monitoring results give people a good idea of the water quality.
However, people still needed to think twice before swimming after heavy rain, said Dr Jarrod Walker, a senior marine scientist at Auckland Council.
"Even a low risk beach can be unsuitable to swim at from time to time and we recommend that you avoid swimming for 48 hours after heavy rainfall."
Based on the last three years of enterococci data, the majority of monitored beaches were suitable for swimming, said Dr Jarrod Walker.
Sixty-four per cent of monitored beaches were classified as having a low or very low risk of causing infection or illness, while 14 per cent were classified as high risk and the remainder are within acceptable limits.
Eleven sites in Auckland - including Fosters Bay, Huia Beach, Te Atatu Beach and Christmas Beach - had an overall "caution" recreation risk, meaning at times the sites could be high risk, although the most recent single samples of some had shown acceptable levels.
Dr Smith said he wanted the millions of Kiwis who go to the beach to swim, surf and play to have access to good information on water quality.
"It enables people to stay healthy and raises awareness of the importance of improving our water quality."
LAWA began in March this year with monitoring data of more than 1100 river sites around the country, but today was being extended to include coastal waters.
The initiative had been jointly created between regional councils, the Cawthron Institute, the Ministry for the Environment and the Tindall Foundation.
"Beaches are a key part of many New Zealanders' lifestyles and it's important that people can swim without getting sick from contaminated water," Dr Walker said.
"By reviewing bacteria levels at beaches over time, LAWA allows us to assess to what extent the water at our beaches is affected by bacteria and whether this poses a health risk to the public."
He also advised people to remember LAWA provides information on water quality but other hazards may be present.
"Our natural environment is a great playground but can be unpredictable. People need to be aware of the other potential risks such as rips or currents before jumping in."
Fran Wilde, chair of the Local Government New Zealand regional sector group, said the response to river data that had been available on the LAWA website had been so far positive.
"It's great to be able to build on the information available and move into the marine environment and we're excited to provide beach information on LAWA in time for summer when our beaches are at their busiest."
Ms Wilde said work on other environmental indicators for LAWA is ongoing and the website will eventually show information on water quantity, air quality, land and biodiversity, as well as more fresh and coastal water quality data.
LAWA would also contribute to a new national environmental reporting regime being designed by the Ministry for the Environment and Statistics New Zealand.
Meanwhile, Dr Smith said the Government would next year be passing a new Environmental Reporting Act through Parliament to expand the quality and quantity of data.
"This work is about giving integrity to New Zealand's clean green brand and highlighting areas where communities need to do better in managing water quality."