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Monitoring of freshwater swimming spots

Which sites are monitored?

Regional and district councils monitor water quality at around 200 freshwater sites throughout New Zealand every summer. It is impossible to monitor all recreational sites. Criteria for identifying which sites to monitor varies from region to region but is generally based on the extent of recreational use, historical knowledge of water quality in an area and the activities affecting it. The 200 monitored sites are in lakes and rivers where water-based activities such as swimming and water-skiing are common.

How are sites monitored?

Water samples are typically taken once a week over the summer (usually November to March) and tested for Escherichia coli (E. coli) bacteria. Testing the water for all possible contaminants would be expensive and impractical. Instead, E. coli are used which do not necessarily cause human disease themselves but indicate the possible presence of other disease-causing organisms. Included in the group of disease-causing micro-organisms are bacteria, viruses and protozoa - these are present in the faeces of warm-blooded animals including wild animals such as birds, deer, possums, pigs and livestock and humans. There are other contaminants which can make recreational sites unsafe to swim at (eg, toxins from algal blooms). These other contaminants are not covered by this monitoring.

Learn more about the water quality guidelines used for freshwater recreational areas.

Compliance for samples from lakes and rivers is based on the ‘action’ threshold from the guidelines for contact recreation, of 550 E. coli per 100 millilitres of water sampled.

The water quality at individual sites is often reported by regional and district councils on their websites and in their annual environmental reports. When E. coli levels are higher than those recommended by the guidelines for contact recreation, councils liaise with health authorities to ensure the public is warned (by signs or other means) there is an unacceptable health risk if they enter the water.

Want to know more about monitoring in your area?

Information on recreational water quality monitoring and results in your area.

What are the public health risks?

Micro-organisms such as viruses, bacteria and protozoa, are present in all natural water bodies. Water contaminated by faecal micro-organisms may pose a human health hazard, particularly if swallowed. Everybody can be affected but small children, the elderly and people already weakened by illness or fatigue are more likely to become ill from exposure to contaminated water.

In most cases the health effects of exposure to contaminated water are minor and short-lived. The most common illnesses are those of the gastric-intestinal system, leading to symptoms like diarrhoea or vomiting and infections of the eye, ear, nose and throat. However, there are other, potentially more harmful diseases such as giardiasis, cryptosporidiosis, campylobacteriosis and salmonellosis. Hepatitis A can be contracted from contaminants in the water and can lead to long-term health problems.

How has council data been used for national reporting?

The national data set presented here has been compiled from weekly water quality sampling results provided by the regional councils and territorial authorities. These samples are considered to represent a snapshot of beach water quality.

The 'current situation' is based on data from 300 freshwater sites, which had at least 10 samples collected over the 2007-2008 and 2008-2009 summers in total.

The 'recent trend' is based on data from about 200 freshwater sites - only those where at least 10 water quality samples are taken over a single summer. The number of sites varies from year to year as regional monitoring programmes change. For example, the summer with the fewest monitored sites (153) was 2003-2004 and the summer with the most monitored sites (230) was 2006-2007.

Return to the water quality at freshwater swimming spots page.

Last updated: 29 June 2009