Frequently asked questions
- About the monitoring program
- What are the ratings?
- When and how do the weekly general condition ratings change?
- Swimming in the Lower Yarra River section
- E.coli
- Indicator bacteria
- Primary contact
- Secondary contact
- Geometric mean
- Sources of contamination
- Health risks associated with recreational waters
- Other programs
About the monitoring program
Weekly water quality sampling for E.coli at 12 sites on the Yarra River from Docklands to Warburton is undertaken by Melbourne Water. The site locations are provided in the table below. These E.coli results are used by EPA Victoria to provide the weekly update of the condition at each site.
| Site name | Site location |
|---|---|
| Docklands | Flinders Wharf, upstream of Charles Grimes Bridge
In December 2006, construction activities restricted access to the original Docklands site. From January 2007 this site has been relocated 200 metres upstream to Flinders Wharf. |
| Southgate | Princes Bridge |
| South Yarra | Pier downstream of Prahran Main Drain |
| Abbotsford | Johnston Street Bridge |
| Kew | Chandler Highway Bridge, Kew |
| Heidelberg | Banksia Street Bridge |
| Templestowe | Fitzsimmons Lane Bridge |
| Warrandyte | Warrandyte Road Bridge |
| Coldstream | Spadonis Reserve |
| Healesville | Everard Park Canoe Ramp, Maroondah Highway |
| Launching Place | Don Road Bridge, Launching Place |
| Millgrove (Warburton) | Dee Road Bridge, Millgrove |
What are the ratings?
Each site has been given a water quality condition rating, calculated using the results of weekly bacteria samples. The rating is based on a statistical average of E.coli (the geometric mean) over the last five samples. This average is compared to rating categories based on Victoria's current environmental quality objectives for primary and secondary contact recreation. To give users current information on recreational water quality, the ratings are based on samples taken under all weather conditions and are updated weekly.
The ratings are indications of recreational water quality over the previous five weeks, and do not give a measure of risk to the health of river users on any given day. River users should take care at all times and not swallow river water. They should also be mindful of other potential hazards such as high flows, unseen objects and litter.
The rating system has four categories:
High water quality - The E.coli geometric mean, based on the last five samples, has remained below the primary contact objective of 200 organisms per 100mL. These sites are generally considered suitable for all forms of recreation. Although the water quality is high, there may still be some potential health risk for some people. On occasions, such as after high rainfall, there may be an increased possibility of contamination from runoff, which may contain animal or human waste.
Medium water quality - The E.coli geometric mean, based on the last five samples, is in the range between 201 and 1000 organisms per 100mL. Sites with water quality in this range are considered suitable for boating, but not generally suitable for swimming. There is a potential health risk for some people from exposure to the water, particularly if swallowed. High rainfall events may increase the risk of contamination from animal or human waste.
Low water quality - The E.coli geometric mean, based on the last five samples, is in the range between 1001 and 5000 organisms per 100mL. Sites with water quality in this range may be used for boating, but they are not suitable for swimming. There is a greater potential health risk to river users from exposure to the water, particularly if swallowed. High rainfall events may further increase the risk of contamination from animal or human waste.
Unsuitable for recreation - The E.coli geometric mean, based on the last five samples, is greater than 5000 organisms per 100mL. Sites with water quality in this range are considered unsuitable for recreational activities, with a greatly increased potential risk to human health. This rating will remain in place until the E.coli geometric mean returns to below 5000 organisms per 100mL.
In addition to the condition rating for each site, EPA will issue alerts or advisories when required:
River user's alert - In the event of a pollution incident or single, very high E.coli result, that could affect the recreational water quality of the river. The alert will remain in place until E.coli levels in follow up samples return to a range considered suitable for recreational activities.
Stormwater advisory - If high rainfall events occur that may affect the recreational water quality of the river. EPA monitors rainfall at gauges throughout the catchment. When rainfall exceeds 20mm over the previous 48 hour period in the Lower and Middle Yarra or 40mm over the previous 48 hours in the Upper Yarra, a stormwater advisory will be issued. The advisory will apply to individual sections of the river, Lower, Middle or Upper, if rainfall has been localised, or to the entire river if rainfall is widespread. The advisory will be removed when conditions return to those considered suitable for recreational activities, usually around five days after heavy rain ceases.
When and how do the weekly general condition ratings change?
EPA reviews the weekly E.coli data and calculates a geometric mean based on the last five samples. The geometric mean is used to set a weekly rating for a site. These ratings may change each week, reflecting the change in weekly E.coli results.
For example, if the general condition rating is high (generally suitable for all forms of recreation) and a storm event or pollution incident significantly increases E.coli levels in the weekly sample, then the rating might be downgraded to medium (suitable for boating activities, but not suitable for swimming) or low (less suitable for boating activities and unsuitable for swimming) until E.coli levels return to levels normally found at the site.
In addition to changed ratings at a site, a stormwater advisory or a river user's alert will be posted on the Yarra Watch website when there is significant rainfall or if there is a very high weekly result or pollution incident, respectively. These advisories and alerts reflect a change in the suitability of the river for recreational activities.
Swimming in the Lower Yarra River section
Swimming is regulated in the lower section of the Yarra River for safety related reasons due to boating activity in that stretch of the river. Under the Marine Act (1988) and its regulations, the waters of the Yarra River upstream of the port of Port Phillip (Bolte Bridge) to the Gipps Street Bridge (Collins Bridge) in Collingwood are prohibited to swimmers.
Permits are available for designated events and are administered by Parks Victoria.
E.coli
E.coli (Escherischia coli) is the indicator bacteria currently used by EPA Victoria to assess the recreational water quality of rivers and streams.
E.coli are bacteria that are present in high numbers in the intestinal tracts of almost all warm-blooded animals, are always present in faecal waste and are easy to detect and measure. Since E.coli occur in faecal waste, they are used to indicate the presence of other pathogenic (disease causing) micro-organisms that pose a health risk to humans. E.coli are used because it is very difficult to detect pathogens which may be present in very small numbers in the aquatic environment. E.coli are generally harmless to humans, however a small number of strains have been known to cause disease.
Indicator bacteria
Bacteria, protozoa and viruses can be difficult to sample and measure. They may be present in very low numbers, and the tests for some pathogens are very difficult, time-consuming and expensive. Indicator organisms, such as E.coli, are chosen because they also live in human and animal digestive systems, and are easily and quickly measured.
E.coli are not usually harmful themselves, however their presence may indicate that pathogenic (disease causing) bacteria, viruses or protozoans may also be present. It is important to be aware that although the presence of high levels of E.coli can indicate recent faecal contamination, low numbers of E.coli do not necessarily mean that there is no risk of illness through contact with water.
Primary contact
Primary contact recreational activities include swimming, water skiing and diving. The user comes into direct contact with the water by immersion or through frequent wetting of the face by water spray, and some water may be swallowed.
The State recreational water quality objective for primary contact is a geometric mean of less than 200 E.coli organisms/100mL of water. The objective is a statistical average, and individual E.coli measurements may be above these objectives, without necessarily affecting the overall suitability of the river for recreational purposes.
Recreational water that meets the primary contact objective is generally considered suitable for swimming, however, there may still be risks of illness at this level for some individuals, particularly the young, the elderly or those with reduced immunity.
Secondary contact
Secondary contact recreational activities include boating, wading and fishing. There is less frequent body contact with the water and little likelihood of swallowing or inhaling water.
The State recreational water quality objective for secondary contact is a geometric mean of less than 1000 E.coli organisms/100mL of water. The objective is a statistical average, and individual E.coli measurements may be above these objectives, without necessarily affecting the overall suitability of the river for recreational purposes.
Recreational water that meets the secondary contact objective is considered suitable for boating actvities, however generally unsuitable for swimming. Higher levels of E.coli may indicate an elevated risk to the health of individuals, especially the young, the elderly or those with reduced immunity, depending on the degree of contact with the water.
Geometric mean
A geometric mean is a type of statistical average that minimises the effects of both high and low values. It is used as a standard statistical measure for assessing changes in recreational water quality over time by environment agencies across the world. EPA Victoria calculates the annual geometric mean using all E.coli sample results over the course of each calendar year. The weekly condition ratings reported on Yarra Watch are derived from geometric means calculated using the five most recent E.coli weekly samples to give an indication of current recreational water quality.
The geometric mean is an average of data collected over a period of time and not an absolute or maximum limit for E.coli. Individual measurements of E.coli are expected to vary, and may be either above or below the recreational water quality numerical objective for primary or secondary contact, without necessarily affecting the overall suitability of the river for recreational purposes.
Sources of contamination
All waterways contain micro-organisms. They are a natural part of the environment, and also occur in human and animal faecal waste. Some of these organisms can cause disease in humans and are known as pathogens. The presence of pathogens from faecal waste in waterways may result in illnesses in some people who come in contact with contaminated water. Whether or not someone gets sick is dependant on a range of factors, including the nature and duration of exposure, and an individual's susceptibility to the particular pathogen present.
Potential sources of faecal contamination to urban waterways such as the Yarra River include sewage overflows, leaking sewerage pipes, illegal sewerage connections, poorly operating septic tanks, agricultural and stormwater runoff. Contamination may also originate from pets, wildlife and livestock, as well as from people using the river themselves for recreation activities.
In very wet weather, the sewer emergency relief structures (ERS) may allow temporary discharge of sewage into creeks and stormwater drains. Also, non-human faecal contamination may also enter the river system via runoff into storm water drains and surface runoff direct to the river. In dry weather, there should be no sewage overflows, and the identification of sources and origins of faecal pollution is more difficult. Dry weather sources may include domestic and agricultural animals, seepage from collapsed pipes or poor or illegal connections.
Health risks associated with recreational waters
Micro-organisms, including bacteria and protozoa are a natural part of every environment, including pristine rivers and streams. As a river flows through urban, forested or agricultural land to the sea, runoff from the land and water from tributaries adds to the number of micro-organisms that the river contains. Water contaminated with faecal material from humans or animals may carry pathogens which pose a risk to river users. In most cases, any health effects from contact with recreational waters will be mild and short lived, however occasionally more severe illness can occur.
The level of health risk for river users depends on the degree of contamination, the amount and type of contact with the water and the age and state of health of people exposed to the water. The very young, the elderly and people with impaired immune systems may be more at risk from some types of water borne infection.
Further information on the health risks of recreational waters is available:
- Victorian Government Health Information: Recreational waterways
- NHMRC Guidelines for Managing Risks in Recreational Water (June 2006) - Please go to Chapter 5: Microbial Quality of Recreational Water and Chapter 5.2: Health effects associated with faecal pollution (Adobe PDF file, 1750KB or 1.75MB)
Other programs
- Sources and origins of faecal contamination in the Yarra River
Ongoing improvements in bacterial water quality require the identification and quantification of origins and sources of faecal matter to the Yarra River from both major input streams and stormwater drains. This is necessary to allow the direction of management action and resource investment to areas where they will have the maximum benefit in reducing faecal contamination inputs to the Yarra.
EPA is leading a three-year program, conducted by Melbourne Water, to investigate the likely origins and sources of faecal contamination in the lower and middle reaches of the Yarra River, identify and target priority source clean-up measures and management actions.
- Bacterial indicators and objectives
As with all things, understanding continues to develop as knowledge increases. EPA, together with the Department of Human Services, will investigate new and emerging approaches for assessing bacterial contamination. Over time, this may result in changes to limits, indicators or the assessment approach for recreational water quality in rivers.