What Affects River Health?
Ever since the early years of European settlement, human development has altered our rivers and creeks.
Gone is the time when the Yarra was used as an open drain for household waste and a dumping ground for industry. Now stormwater pollution is the major scourge, with about 500 billion litres a year of water containing contaminants and litter washed down the drains into rivers, creeks and bays.
Litter
Litter is the most visible component of stormwater pollution. When it rains, litter gets washed from streets and buildings down stormwater drains and into our rivers and creeks.
Litter not only looks unsightly, but is also a real threat to the health of animals, plants and fish living in our waterways.
Parks Victoria operate 14 litter traps on the Yarra, which collect about 1800 cubic metres of litter, debris and organic matter washed into the river each year. This includes plastic and glass bottles, syringes, drink cartons, cigarette butts and lighters, most of which come from commercial and industrial areas and building sites.
Melbourne Water and Parks Victoria work collaboratively on litter removal along the Yarra, however we all have a responsibility to dispose of our litter correctly.
Pathogens
Because our rivers are open systems, various microorganisms can be washed into them from rural catchments and our highly populated city.
Even pristine rivers will contain some microorganisms, which is why people using rivers for recreation should use commonsense. Many microorganisms are harmless, but some can cause disease in humans and are called pathogens.
Potential sources of pathogens in urban waterways such as the Yarra River include human and animal faecal waste. These enter via stormwater, poorly maintained septic tanks, sewage overflows and animals in the catchment.
As Melbourne’s sewerage system has continued to be upgraded, levels of E. coli in the Lower Yarra have fallen. (The bacterium E. coli is an indicator of recent faecal contamination). But in the past decade, these levels have not changed significantly. This is an indication of water quality and catchment management works keeping pace with population growth and development.
Water quality in the Lower Yarra is monitored weekly for E. coli, an indicator for faecal contamination. E. coli levels in the Yarra River compare well with other urban rivers around the world.
The EPA advises against water-based recreational activities within five days of heavy rain, as there may be increased pollution due to stormwater run-off.
The Department of Human Services provides public health information for using recreational waterways safely. Visit their website at www.health.vic.gov.au/environment/water/rec_water.htm
Swimming is not permitted in the Lower Yarra due to the danger posed by boats.
Toxicants
Stormwater also contains contaminants such as petroleum hydrocarbons from fuel and engine oil, heavy metals such as zinc, lead, copper, chromium and lead (much of which is washed off roofs and roads or comes from poor management of industrial sites), as well as animal droppings.
Nitrogen
Nitrogen is a widely distributed natural element in the atmosphere and water, and is found in large amounts in stormwater. Although nitrogen has a vital role in providing plants and animals with food for growth, in excessive amounts or in certain compounds it causes vigorous growth of plants, including algae, which leads to a depletion of oxygen levels in water.
A 1996 CSIRO study sponsored by Melbourne Water recommended that the amount of nitrogen entering the Bay from stormwater and treated effluent be reduced by 1000 tonnes a year.
Melbourne Water will contribute to this target by constructing wetlands, which act as natural filters by removing nitrogen, litter and suspended solids from stormwater.
Melbourne Water manages 99 wetlands, and invests about $5.6 million a year building wetlands. Melbourne Water’s contribution to this target will be achieved through upgrading the Western Treatment Plant and constructing wetlands, which act as filters for Melbourne’s stormwater.