Testing and grading

Regional councils – and district councils in some areas – are responsible for monitoring swimming-water quality.

Coastal sites are tested for enterococci (levels above 280 enterococci per 100mls of water are considered “unsafe” to swim). Freshwater sites are tested for e.coli (levels above 550 e.coli per 100mls of water are considered “unsafe”).

Enterococci and e.coli thresholds are set in national guidelines and are based on an “acceptable risk” of getting sick. For coastal sites, the acceptable level of risk is set at 19 in every 1000 bathers falling ill; for freshwater sites, it’s 8 in every 1000.

Not every swimming spot around the country is monitored. Councils may also stop monitoring a site if testing shows water quality is either consistently poor or consistently good. Sites permanently unsafe for swimming should have a warning sign. Any spot may also be unsafe for swimming if it’s been raining. The risk of getting ill can remain high for several days after rainfall.

Swimming in polluted water can cause skin, eye and ear infections as well as cold- and flu-like symptoms. It can also cause nasty gastrointestinal diseases such as the one caused by campylobacter. Campylobacter has been found consistently in river-water samples.

Beach grades

National water-quality guidelines recommend that councils grade each of the swimming spots they monitor. These "beach grades" are based on long-term faecal-indicator counts and an assessment of a site’s susceptibility to contamination. They range from “very good” to “very poor”.

However, only some councils use the grading system. We've collected data from those that do (see Graded swimming sites). Grades were correct as at December 2010.

Only 20 percent of the 445 graded sites get the top mark of “very good”. Another 31 percent rate “good” and just over a fifth (23 percent) manage a “fair” grade. 26 percent rate either “poor” or “very poor” – most of these are freshwater sites on rivers and streams where water quality is compromised by agricultural and other land uses. 

The 5 grades

• Very good: Satisfactory for swimming at all times and may not require monitoring on a regular basis.
• Good: Satisfactory for swimming most of the time. These sites are monitored throughout the summer; councils are meant to put up warning signs if water quality deteriorates.
• Fair: Generally satisfactory for swimming but have many potential sources of faecal material. Be cautious about swimming during periods of high rainfall - and don't swim if the water is discoloured.
• Poor: Avoid swimming. This applies especially to the very young, the very old and those with compromised immune systems. These sites are likely to have permanent warning signs, but the council may instead monitor the sites once a week and put up temporary warnings.
• Very poor: Avoid swimming - there are direct discharges of faecal material. The council is meant to put up a permanent sign that says swimming is not recommended.