Greater Wellington's bathing water quality monitoring programme
Recreational (bathing) water quality monitoring is currently undertaken at 21 freshwater and 77 marine sites across the Wellington region. Since the 2000/2001 summer, monitoring has been a joint effort involving Greater Wellington and its constituent local councils, in particular the Kapiti Coast District Council, Porirua City Council, Hutt City Council, and Wellington City Council. Regional Public Health and Wairarapa Public Health are consulted on occasions when the results of the monitoring indicate a serious health risk might exist.
Why do we monitor?
Greater Wellington and city and district councils monitor recreational water quality to identify risks to public health from disease-causing organisms and advise the public of these risks. People can then make informed decisions about where, when, and how they use rivers and the marine environment for recreation.
In addition to assisting with safeguarding public health and the environment, Greater Wellington's recreational water quality monitoring programme also serves to:
- Provide a mechanism to determine the effectiveness of regional plans;
- Provide information to assist in the determination of spatial and temporal changes in the environment (State of the Environment (SoE) monitoring); and
- Provide information to assist in targeted investigations where remedial action or mitigation of poor water quality is desired
What do we monitor and why?
On each monitoring occasion a single water sample is collected from the bathing site and analysed for Escherichia coli (fresh waters) or enterococci (marine waters) indicator bacteria. These bacteriological indicators are associated with the gut of warm-blooded animals so their presence in the water samples indicates the risk of faecal contamination and therefore the potential presence of harmful pathogens.
Measurements of water temperature and turbidity, and visual estimates of periphyton (algae) cover, are also made at each freshwater site. Excessive amounts of periphyton, in particular filamentous algae, can reduce the amenity value of waterways by decreasing their aesthetic appearance, reducing visibility, and being a physical nuisance to swimmers. Algae can also grow as thick mats on the riverbed. Under certain conditions that are not yet well understood, mats of blue-green algae (cyanobacteria) have the potential to release toxins that may be harmful to animals and humans.
At marine bathing sites, observations of weather (in particular wind) and the state of the tide, and visual estimates of seaweed cover, are also made to assist with the interpretation of the monitoring results. For example:
- Rainfall may increase enterococci counts by flushing accumulated debris from urban and agricultural areas into coastal waters.
- Wind direction and strength can influence the movement of currents along the coastline and can therefore affect water quality at a particular site.
- In some cases, an increase in enterococci counts may be due to the presence of seaweed. Under warm conditions when seaweed is excessively photosynthesising or decaying, enterococci may feed off the decayed seaweed or increased carbonaceous material produced by the seaweed during photosynthesis.
At both freshwater and marine bathing sites, an estimate of the rainfall in the catchment adjoining each site can also be made by obtaining records from the nearest rain gauge. Rainfall can have a significant impact on