Dr Ralph Ogden

ACT Healthy Waterways Program Manager

Lake Tuggeranong has elevated nutrient levels that cause blue-green algal blooms in the warmer months, creating health risks and reducing the amenity values of the lake. The source of the problem is excessive phosphorus loading annually from stormwater drainage. The ACT Healthy Waterways program has now drafted a plan, underpinned by three technical reports, that suggests it is possible to implement phosphorus pollution mitigation activities and works to avoid excessive nutrient enrichment of the lake—and blue-green algal blooms—in an average of three out of four years. The draft plan therefore sets a ten-year vision that by 2035, Lake Tuggeranong is more consistently free of blue-green algal blooms, and when they do occur, they are short-lived. The draft plan presents potential options for mitigating phosphorus levels in stormwater. The most cost-effective of these are an increased frequency of street sweeping and building constructed wetlands to treat polluted stormwater. However, no option is a ‘silver bullet’ that has the potential to reach the phosphorus mitigation target on its own. Even with significant investment in mitigating phosphorus pollution, we cannot prevent algal blooms in all summers. We may need to be develop options to treat algal blooms as they arise in the summers where pollution levels permit their formation. This talk presents the approach we took to identify solutions to the problem, key results from our analyses, and some of the political and practical lessons learned from the project in the context of the broader, ten-year ACT Healthy Waterways program.