Recreational water quality is important for health
Many New Zealanders enjoy swimming at coastal beaches and in rivers and lakes.
However, recreational waterways can become contaminated with faecal pathogens (such as bacteria and viruses) from human sewage and animal manure. These pathogens can cause [1-5]:
- gastrointestinal illnesses (causing diarrhoea and vomiting)
- respiratory diseases
- eye, ear, nose and throat infections.
Anyone may be affected, but young children, older adults and people with weakened immune systems are more vulnerable.
More harmful diseases like Hepatitis A can also be contracted from contaminants in the water.
Algal blooms can also cause illnesses through contaminated shellfish or toxins produced by cyanobacteria.
The most common water-related gastrointestinal illnesses are campylobacteriosis, cryptosporidiosis and giardiasis.
- Campylobacteriosis is caused by a bacterium, usually Campylobacter jejuni or C. coli . Symptoms include abdominal pain, fever and diarrhoea, often with bloody stools.
- Cryptosporidiosis is caused by the intestinal parasite Cryptosporidium . Cryptosporidiosis is an acute illness characterised by diarrhoea and abdominal pain.
- Giardiasis is caused by the protozoan parasite Giardia intestinalis. The main symptoms are diarrhoea and cramps.
These gastrointestinal illnesses can be contracted in various ways, including contact with contaminated water, farm animals, sick animals, faecal matter, other symptomatic people, and eating contaminated food .
The origins of waterborne pathogens
The two major sources of waterborne faecal pathogens in New Zealand recreational waters are human sewage and animal manure.
Most human sewage in New Zealand is processed in sewage treatment systems, then discharged into water . Not all sewage treatment systems carry out tertiary treatment to disinfect the wastewater and kill pathogens. Untreated sewage may also get into waterways through broken sewer pipes, storm overflows and poorly maintained septic tanks.
Animal manure includes faecal matter (or effluent) from livestock, such as cattle, deer and sheep. Rainfall can wash livestock faecal matter from farmland into waterways. Contamination can also occur if livestock are allowed to defecate directly into streams. Animals like waterfowl, ducks and dogs may also contaminate water in some localised areas.
How waterways become contaminated
In general, contaminants can pass into rivers, lakes or coastal waters through either:
- point source discharges (e.g. discharges of treated wastewater)
- diffuse source pollution (e.g. run-off from agricultural land).
Point source discharges come from a single point, such as a pipe. Large efforts have been made over the past 40 years to control point source discharges in New Zealand . For example, many sewage treatment plants have been upgraded to control or eliminate any discharges into the local environment.
Diffuse (or non-point) source pollution, in which contaminants leach into a water source across a wider area, are now considered the main source of water pollution in New Zealand [10,11]. These diffuse sources are mainly associated with intensive land use, particularly agricultural production .
How livestock faecal matter can affect water quality
Faecal matter from livestock can get into waterways in a number of ways, such as:
- rainfall washing livestock effluent from the land into waterways
- livestock defecating directly into waterways (if they have access)
- leaching into groundwater
- illegal discharges of effluent from milking sheds or piggeries directly into waterways.
Effluent from milking sheds is often irrigated back onto the farmland. In some cases this effluent may still enter waterways, if:
- rainfall washes away dairy effluent after it is deposited onto pasture
- the ground is too wet for the irrigated effluent to soak in
- effluent storage ponds overflow.
Bacteria levels in waterways are often highest after rainfall, when faecal matter is carried from land into the waterways.
Read more on the livestock webpage.
Some waterways are more at risk of becoming polluted
Freshwater sites, like rivers and lakes, are more vulnerable to water contamination than coastal beaches.
This is because contaminants are more rapidly dispersed by currents and diluted by larger volumes of water at coastal beaches .
As a result, freshwater sites are generally more likely than coastal sites to have higher background levels of bacteria, as well as longer-lasting and more frequent contamination events.
1. Ministry for the Environment. 2003. Microbiological Water Quality Guidelines for Marine and Freshwater Recreational Areas. Wellington: Ministry for the Environment.
2. Corbett S J, Rubin G L, Curry G K, Kleinbaum DG. 1993. The health effects of swimming at Sydney beaches. The Sydney Beach Users Study Advisory Group. American Journal of Public Health 83(12): 1701-1706.
3. Harrington J, Wilcox D, Giles P, Ashbolt N, Evans J, Kirton H. 1993. The health of Sydney surfers: an epidemiological study. Water Science & Technology 27(3-4): 175-181.
4. McBride G, Salmond C, Bandaranayake D, Turner S, Lewis G, Till D. 1998. Health effects of marine bathing in New Zealand. International Journal of Environmental Health Research 8(3): 173-189.
5. World Health Organization. 2003. Guidelines for safe recreational water environments: Coastal and fresh waters (Vol. 1). World Health Organization.
6. World Health Organization. 2014. Water-related diseases: campylobacteriosis. Retrieved 21/09/2016, from http://www.who.int/water_sanitation_health/diseases/campylobacteriosis/en/
7. World Health Organization. 2013. Preventing cryptosporidiosis: the need for safe drinking water. Retrieved 06/05/2014, from http://www.who.int/bulletin/volumes/91/4/13-119990/en/
8. ESR. 2014. Notifiable and Other Diseases in New Zealand: Annual Report 2013. Porirua, New Zealand. Available online: https://surv.esr.cri.nz/surveillance/annual_surveillance.php
9. PCE. 2012. Water Quality in New Zealand: Understanding the science. Wellington: Parliamentary Commissioner for the Environment.
10. Howard-Williams C, Davies-Colley R, Rutherford K, Wilcock R. 2010. Diffuse pollution and freshwater degradation: New Zealand perspectives. Paper presented at the 14th International Conference of the IWA Diffuse Pollution Specialist Group, DIPCON 2010, Québec City.
11. Proffitt F. 2010. How clean are our rivers? Retrieved 1 August 2014, from http://www.niwa.co.nz/publications/wa/water-atmosphere-1-july-2010/how-clean-are-our-rivers
12. Ministry for the Environment. 2007. Environment New Zealand 2007. Wellington: Ministry for the Environment.
13. Ministry for the Environment. 2013. Suitability for swimming. Available online: http://www.mfe.govt.nz/environmental-reporting/fresh-water/suitability-for-swimming-indicator/suitability-swimming-indicator.html