Duckweed covers River Torrens, turns water green

The River Torrens has gone green – but Adelaide City Council says it is nothing to be concerned about.

A stretch of the River Torrens has become a slimy green eyesore, thanks to an infestation of duckweed.

The aquatic plant, which grows rapidly and is packed with nutrients, has blanketed the river near Hackney Rd.

Adelaide City Council associate director Ross Whitfield said duckweed, also known as macrophytes, posed no health problems.

Green duckweed covers the River Torrens in Adelaide, near Hackney Road. Picture: Kelly Barnes

“The regeneration of these macrophytes has been a long-term goal of the council since the river was dredged in the ‘90s and all macrophytes perished,” Mr Whitfield said.

“The plants actually play a very important role in restoring river/lake health and are part of a natural river system.”

Mr Whitfield said the duckweed would only be removed if necessary.

“We do remove the duckweed when it builds up too much by using boats to net the plant into a confined space, then we use trucks to vacuum it out of the water.”

The duckweed is a food source for both ducks and carp, and also discourages the growth of blue-green algal blooms.

Bright-green duckweed covers the River Torrens in Adelaide, near Hackney Road. Picture: Kelly Barnes

In December 2021, the Torrens Lake showed a rapid increase in blue-green algae concentrations, so freshwater was released from Kangaroo Creek Reservoir to improve water quality.

In March, The Advertiser reported that duckweed could be the key to producing food for astronauts undertaking long journeys in space.