Take me to the river
The postponement of the swimming portion of the men’s Olympic triathlon due to pollution in the River Seine reinforces the importance of basing decisions about water quality on evidence.
The idea that Melbourne’s Yarra River water quality, for example, can be made consistently safe for swimming is likely to encourage dangerous activity, based on inadequate understanding of monitoring results.
The presence of E. coli bacteria in the water does indicate recent faecal pollution but not necessarily the presence of more persistent disease risks. Protozoans such as Cryptosporidium and Giardia may cause serious illness. The presence of protozoans in the river is not reliably indicated by E. coli and they are not usually included in routine monitoring programs.
Basing decisions about swimming on occasional grab samples is like deciding to cross a street blindfolded because there was no traffic in a photo taken somewhere else at another time.
Of course we should work towards improving water quality in our waterways. The lower Yarra in Melbourne resembled a sewer not long after European settlement and a great deal has been achieved to restore the river in recent times, including the improvement of the Werribee and Southeastern treatment plants and their associated infrastructure.
Unlike the Seine, the Lower Yarra is estuarine with a salt ‘wedge’ extending upstream to Dights Falls, as the rocky reef adjacent to Spencer Street in the CBD which once impeded the salt wedge has long since been removed.
French authorities have reportedly spent $1.5 billion on improving water quality in the Seine for the Olympics. Much of this expenditure has been for sewage disinfection and stormwater retention and treatment. Measurable improvement has been achieved in terms of E. coli; however, one scoop of dog poop is enough to raise the E. coli count in an Olympic pool from zero to above the WHO limit for swimming.
Cyanobacteria (Blue-Green Algae) are notoriously difficult to control, for instance, and may also pose a serious risk to swimmers. The diffuse source nutrients that drive BGA outbreaks can only be removed by advanced treatment, which is not practical for stormwater and the cost is prohibitive.
For Melbourne’s beaches, E. coli is even less reliable as an indicator of harmful pollution levels in saline waters, including the Lower Yarra where the water’s salinity varies, sometimes rapidly, with depth and distance, depending on flow and other factors. Obtaining representative samples is therefore problematic.
I therefore do not think the responsible health authorities will be able to declare the Lower Yarra safe for swimming, even with a much more comprehensive and expensive monitoring system.
Gold mining, forestry, transport, building and agriculture all had major impacts on water quality across the state. So, the water quality issue goes well beyond the Yarra catchment.
Given scarce resources, the opportunity costs of disproportionate spending on the Yarra for swimming are the impacts of neglecting water quality, environmental improvements, ecological values and economic infrastructure more generally throughout Victoria.
Spending large sums on improving the water quality in the Yarra to render swimming safe may therefore not be the best allocation of effort and funds.
Max Thomas, Dip. Agric. (retired) worked in the public sector and in private consulting on a range of land, water and waste management projects. He prepared guidelines for irrigation with recycled water for EPA Victoria and developed a number of Environmental Management Systems in the water industry.
