Removal of rotting seagrass in Swan River a last resort, despite bad smell


Seaweed at Point Walter.
Seaweed at Point Walter.

A BAD odour caused by rotting seagrass in the Swan River will only be dealt with as a last resort, the Department of Biodiversity, Conservation and Attractions (DBCA) says.

The Department said seagrass and macroalgae often accumulates on shorelines at this time of year, emitting a bad smell as part of the natural breakdown process.

DBCA rivers and estuaries director Mark Cugley said submerged vegetation provided habitat for fish and sea horses and was a food source for black swans.

“Macroalgae and seagrass in the Swan River can grow rapidly at this time of year due to increases in temperature, available light and nutrients,” he said.

“Then, as it dies off, prevailing winds and tides can cause it to accumulate as wrack on some foreshores of the Swan Canning Riverpark.”

Mr Cugley said that while the smell was unpleasant, water movement often disperses the material naturally.

He said the removal of wrack was only carried out as a last resort.

“Where it is practical to remove wrack, it needs to be dry before being taken offsite for disposal and may be stockpiled to dry for several days if required,” he said.

“This decision is made in consultation with local governments, which have a shared responsibility for the foreshore.”

Residents surrounding North Lake experienced their own bad smell in August, with rain helping our dams but doing little for the nose.

People took to social media seeking answers to the cause of the strong smell of faeces affecting people in Kardinya, Winthrop, Melville and even Mt Pleasant.

A DBCA spokeswoman put the bad smell down to the effects of heavy rain at North Lake.

“The area has been investigated and officers have determined that the likely cause of the odour is rotting plant material on the banks of the wetland,” she said.

“The recent above average rainfall has increased the water levels in the wetlands and this has impacted on the fringing vegetation by submerging the grasses and plants, with the plant material beginning to break down and rot over time.

“(This has produced) the associated odour.”The spokeswoman said the odour was more noticeable when large numbers of plants were impacted.

“It is a natural occurrence and the odour should dissipate over the coming days,” she said.

For more information about seagrass and seaweed accumulation, contact the DBCA on 9278 0900.

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