Controlling blue-green algae in the lake has been most successful when releasing flows down the river – high flow rates, for a short duration, mix up and cool down the water – as well as benefiting the whole river system.

These Torrens Lake activities were developed with the support of the Green Adelaide Board, the Department for Environment and Water, City of Adelaide, the Environment Protection Authority and SA Water.

Catchment management• Removed over 3.5 tonnes

of Carp • Erosion prevention and

riverbank planting• Woody weed removal +

replanting with native plants along linear park

• Over 15,000 native aquatic plants placed in the lake

• Regular dredging of the lake, with over 3000m3 removed in 2017

• Fencing-off stock from rural areas

• Major clean up after 2016 storms deposited litter, organic matter and sediment

Monitoring• Every 15 minutes, temperature, dissolved

oxygen and salinity, and weather conditions are measured from 3 permanent water quality monitoring stations in the lake

• Twice weekly water quality monitoring at 7 locations over summer

• Weekly water quality monitoring along the river – including the sea at the outlet

• Twice yearly fish monitoring along the river and around the lake

Hydrogen peroxide trials• Hydrogen peroxide was trialled as it was

known to kill blue-green algae, but not affect other aquatic species

• 2017 and 2018: trials near the zoo • 2016: trial near the weir • 2014 and 2015: trials in the laboratory and

in small ponds

Gulf St Vincent

Adelaide Hills

Windsor Gardens

FelixstowVale Park

Adelaide

Flinders Park

Highbury

AdelaideLockleys

St Peters

Lochiel ParkInfrastructureREMOVING LARGE ITEMS OF RUBBISH• Gross pollutant traps on all stormwater

directly entering the lake• Gross pollutant traps throughout

the catchment, including on First, Second, Third, Fourth and Fifth creeks capturing over 5000 tonnes in the last two years

• Floating boom on the river in St Peters

MINIMISING NUTRIENTS IN THE LAKE• Duck feeding station in the lake closed• Aquatic plants added to take up nutrients • Floating wetlands (aquatic plants grown on a floating platform)

being trialled near Torrens Weir• Phoslock (a chemical that gets rid of phosphorus) trialled in 2006

STORMWATER HARVESTING AND REUSE • First Creek wetland and stormwater reuse scheme created• Linde Reserve biofilter and stormwater reuse scheme created• Felixstow Reserve wetland and stormwater reuse

scheme created

IMPROVING WATER QUALITY• Aerators, to add oxygen to the water, trialled• 2008 and 2012 trials of transportable biofilter

to clean up the water• Flows trialled at different flowrates from

3–5 days, mix up, cool and exchange the water

Torrens Lake update: summer 2020–21The River Torrens and Torrens Lake form one of Adelaide’s most recognisable landscape features. Together they make important social, economic and environmental contributions to the city and the wider metropolitan area.

Each year over summer, water stops flowing into the lake and so it heats up, becoming susceptible to blue-green algae blooms.

Over the past decade, a wide range of initiatives have been trialled in the lake and the broader River Torrens catchment to reduce the frequency and intensity of these blooms, which can discolour water, form scum, and produce unpleasant odours. At a high intensity they can also release toxins that can harm humans and wildlife.

These trials have shown that there is no single solution to reducing blue-green algae growth over summer, and that any long-term, sustainable plan will involve many options and the collaboration of many stakeholders.

So far, regular flows of fresh water into Torrens Lake have been most successful at controlling blue-green algae growth, and keeping the lake open since February 2013. High flows released from Kangaroo Creek reservoir mix up and cool down the water in the lake, successfully disrupting the growth of algae. How much water is released depends on summer weather conditions at the time, such as how hot it is, and the frequency and volume of recent rainfall.

If needed, flows will again be released over summer, timed to counter rising algae levels and minimise beach impacts.

Most flows start on a Friday afternoon from the reservoir, potentially reaching the beach at Henley South late Sunday evening.

The flows continue for up to five days, and the outlet channel is excavated at the beach before each flow to ensure the water heads directly to the sea.

Regular monitoring has shown that the sea is safe to swim in, although advice remains to not swim in discoloured water.

As well as maintaining an open lake over the coming summer, work continues to explore complementary, long-term, sustainable options.

Managing Adelaide’s central jewel over a hot, dry summer